What is the basis that many mainstream Christian groups justify labeling groups like the Mormons and Jehovah Witnesses as Non-Christians?

I'm new here but for more than 45 yrs I have done extensive research on the Bible and related matters.

I. MAINSTREAM BASIS AGAINST LDS & JWs

Mainstream churches generally [very general usage here] believe that they are Bible based. The major reasons given are:

1. a. Most Mainstream churches believe in 1 God with 3 co-equal "heads".

   b. LDS believes there are many Gods.

   c. JWs believe that God & Jesus are separate Gods.

2. a. Most Mainstream churches beleves all believers go to Heaven.

   b. LDS believes believers become Gods & some get their own planets.

   c. JWs think only 144,000 go to Heaven, the rest stay on earth.

3. a. Most Mainstream churches believes Jesus is the Son of God.

   b. LDS believes Satan is Jesus' brother.

   c. JWs believe Jesus is a created being & is now Archangel Michael.

4. a. Most Mainstream churches hold that the Bible is from God (although some add the Apocrypha &/or oral traditions).

   b. LDS's main book is the Book of Mormon along with other extra-biblical books.

   c. JWs have their own Bible, the New World Translation in which verses have been altered or stressed to support their own beliefs.

5. a. Many Mainstream churches hold that Jesus is the only mediator between man and God.

   b. LDS believes that Joseph Smith is a modern day "prophet" who restored the "church" back to its proper place with the truth restored.

   c. JWs have their "Watchtower" Society **Governing Body" providing their scriptural interpretation. They made several wrong prophecies in the 20th century, which they explain away in one way or another.

6. a. The Catholic church (& some related churches) holds that other books and traditions are just as important or even more important to their worship, such as the Apocrypha or lost books and doctrines (i.e. Popes, Infallibility on the throne, Catechism, Assumption of Mary, Immaculate Conception, Veneration of Saints, Rosary, Creeds, etc.) that are beyond the reach of the 66 legitimate Bible books.

   b. LDS beleifs also include books that go beyond the reach of the genuine 66 Bible books. Many of their beliefs have dependancy on the Book of Mormon, Pearls of Great Price and Documents & Covenants, in which it is claimed that gold plates were found in upstate New York, Jesus came to America, Adam & Eve and the Garden of Eden were in Missouri, etc.

   c. JW's have their own Bible in which at least some verses have been altered to support their beliefs. A good deal of their beliefs are dependant on what is written in their Watchtower magazine.

II. REAL BASIS AGAINST LDS & JWs

Actually, the "basis" for what is non Christian is clearly defined in the Bible. The problem is it takes a lot of work to find and lay out a proper, well-defined basis for determining what is and is not rightly Bible based. While many "mainstream" [general broad use here] have determined that neither Mormons (LDS) nor Jehovah Witnesses (JWs) are Christian, a number of them lack true understanding even of their own misinterpretation(s) of what is real Christian teaching (i.e. Trinity Doctrine error -See below under Comment 2).

I believe that to fully answer the posed question requires one to establish a basic set of facts, the Bible foudation & purpose and common sense rules for reasoning out what should be accepted as the truth. Our approach, coming from our human condition, experience from surrounding environmental events and our actions/reactions (cause & effect), our human imperfections (seen and unseen), etc., may make all the difference for drawing a "right" conclusion or failure thereof (we may have to set aside some preconceived ideas, notions, prejudices and/or assumptions). The following might help point us in the right direction:

Since the Bible is the primary reason and basis for Christianity's existence I believe we ought to turn to the Bible to see what it says:

1. BIBLE PROOF

Most important: Is the Bible true?

(ESV) Prov. 30:5 Every word of God proves true; he is a shield to those who take refuge in him.

6 Do not add to his words, lest he rebuke you and you be found a liar.

(most Christian [broad label usage here] and several other religions have stated (or implied) their claims/beliefs are based on, come from the Bible and/or they are associated with the Bible and/or the Bible can be used along with their beliefs/claims and practices but are they wrong? We need to go to the Bible to determine what is true.)

2. JESUS, THE SON of GOD?

The second most important question is: Is Jesus the Son of God or not? Jesus' statement:

John 14:6 Jesus said to him, “I am the way, and the truth, and the life. No one comes to the Father except through me (see Acts 4:12; Jn 5:39).

Either this statement is true or there is no God (He either knows all or He can't be God). In this statement Jesus is making it quite clear that He is much more than just another great teacher. Since Jesus made this statement I thought it is more important to first find out if what He said is true rather than trying to sift through piles of information, books and statements made about Jesus and the Bible.

3. FALSE TEACHERS & PROPHETS

The Bible mentions false prophets (to be a false prophet you must also be a false teacher).

Acts 13:6 When they had gone through the whole island as far as Paphos, they came upon a certain magician, a Jewish false prophet named Bar-Jesus.

2 Peter 2:1 But false prophets also arose among the people, just as there will be false teachers among you, who will secretly bring in destructive heresies, even denying the Master who bought them, bringing upon themselves swift destruction.

Gal 1:8 But even if we or an angel from heaven should preach to you a gospel contrary to the one we preached to you, let him be accursed.

4. JUDGMENT

A proper approach for establishing which is which requires one to find right teaching starting from no. 1 above and also by process of elimination to expose wrong Bible teaching as we find them (if we intend not to be mislead - false teaching has great consequences).

John 7:24 Do not judge by appearances, but judge with right judgment.”

Many believe the Bible says don't judge at all but when carefully read you will find the Bible message actually warns against making wrong or false judgments. Every time you go to cross a street you must judge where and when to cross. All day long we make many judgments as to what we should do.

5. DO NOT ADD OR OMIT THINGS

I found that many do not carefully read what is actually written in the Bible. For instance, many missed the fact that plants were created before the sun and stars. The reason is explained in other Bible text. For every claim made the whole Bible must be taken into context.

1 Cor 4:6 I have applied all these things to myself and Apollos for your benefit, brothers, that you may learn by us not to go beyond what is written, that none of you may be puffed up in favor of one against another.

Gal 3:15 To give a human example, brothers: even with a man-made covenant, no one annuls it or adds to it once it has been ratified.

Deut 4:2 You shall not add to the word that I command you, nor take from it, that you may keep the commandments of the Lord your God that I command you.

6. MAN'S WAYS & IDEAS

I also observed that many make the mistake of believing what others claim is true especially if they have a position perceived as having authority to make such claims.

Jer 10:23 I know, O Lord, that the way of man is not in himself, that it is not in man who walks to direct his steps.;

Prov 14:12 There is a way that SEEMS right to a man, but its end is the way to death.;

Hosea 4:6 My people are destroyed for lack of knowledge; because you have rejected knowledge, I reject you from being a priest to me. And since you have forgotten the law of your God, I also will forget your children.;

Micah 7:5 Put no trust in a neighbor; have no confidence in a friend; guard the doors of your mouth from her who lies in your arms;

Matt 7:21 “Not everyone who says to me, ‘Lord, Lord,’ will enter the kingdom of heaven, but the one who does the will of my Father who is in heaven.

22 On that day many will say to me, ‘Lord, Lord, did we not prophesy in your name, and cast out demons in your name, and do many mighty works in your name?’

23 And then will I declare to them, ‘I never knew you; depart from me, you workers of lawlessness.’

There is a number of other factors, etc. to add to the above but it would take many pages to go into exhaustive detail. I could have spent all my spare time studying all religions to the last detail but filling my head with volumes of useless information, I most likely would never have found out who our God actually is nor who His Son is. There is a verse (I can't remember where it is) that states something like: They gather much knowledge but they'll never find the truth.

Back to the original question: Mormons, JWs and other saw that there was to be a reformation but misunderstood that it was not the New Testament that was at fault (nor the Old Testament either). Mormons, JWs and others did not understand we cannot make up a new "covenant" and that God should honor it. They did not understand that the NT covenant is the final and eternal covenant, superseding all other covenants. Jesus is perfect and so is His new covenant, needing no changes - Both God and Jesus never change. God deliberately set up the old covenant with one major flaw, one that only sending His Son to earth could remedy.

While many "mainstream" churches can readily see the more blatant reasons, "a basis" for why something is wrong with the beliefs of Mormons and Jehovah Witnesses, many do not have a full understanding of why they and others have been and are wrong in many of their beliefs. Perhaps this is a subject for another discussion.

If any claimed "Christian" (again broad usage here) is coloring outside the Bible text and its parameters they are acting outside God's and Jesus' definition and instructions for how to be a genuine Christian in Their eyes. The Bible is all about right and wrong. The wise will keep making it their goal to better comply with its instruction while others will keep looking for justification for whatever suits them, what tickles their ear.

-Edits:

(For comments - Thanks Caleb -I hope this is OK. I added answers because I have a lot to say and some sites do not give one a lot of space to write, more being allowed in an answer.)

Being new here, I can't post a comment so I'm posting more answers (in addition to my original answer) with regard to comments (disreqard -adding it to my original answer).

@ Nelson (1st comment):

I'm not new to LDS beliefs (also, I have even been to the Salt Lake City temple). Before you read my comments please take the time to carefully reread my previous list of Bible references.

Actually, most "standard" Bibles (some are better at doing it) have been mostly properly translated (for the most part, most discrepancies are relatively minor to very minor). Once you become somewhat familiar with the Bible you can compare verses from other versions. However, God is smarter than us and knew some would try to twist the meaning and/or the word itself so He protected His word. He used an unchangeable system (in redundancy) that forever binds the OT&NT truth that never changes.

Other than some mutilation of scripture text (which would make it too obvious that something was done to it at least to the wise), as long as properly translated Bible text exists to be compared to, the truth can't be obscured to those genuinely looking for it.

Whether Joseph Smith was well-meaning or not he added things that were never in the Bible (Jesus was never in America nor were Adam & Eve in Missouri). Any new "vision" must line up exactly with what was written in the Old & New Testament. It cannot vary even one degree. Apparently, Smith was unaware of this.

Jer 23:28 Let the prophet who has a dream tell the dream, but let him who has my word speak my word faithfully. What has straw in common with wheat? declares the Lord.

The fact that the Book of Mormon exists indicates to those who are wise and have even just a good knowledge of the Bible text that it does not conform to what is written in the Bible, that is it is non-Biblical by its very existence. There is no such thing as a God authorized "another testament" nor will there ever be.

The truth is complete, fully contained within the Bible itself. It is why we are warned and instructed to not go beyond what is already written in the Bible itself. Clearly, Smith proves by his writings, whether he intended to or not, that he went far beyond what he thought he perceived as misinterpretation of the Bible text.

The problem is that the more Smith got off in his own direction and misinterpretation the more he compounded the false claims he started with. Whereas, a true reformation would have come by starting with and staying with what was instructed in the Bible. In other words, misinterpretation was because of human error and by their relaxing their guard and/or becoming lazy instead of staying the course, making sure what they taught and did was securely in line with Biblical teaching.

It was not due to the Bible being wrongly translated or just being misinterpreted, which Smith did not understand. Just because you can confess with your lips that Jesus is our Redeemer it does not mean that your heart is not far away from the truth of who Jesus is nor how to follow Him (truly, from within your heart not by more of an outward or mechanical motion or what you think Jesus wants from you or wants you to do).

Isaiah 29:13 And the Lord said: “Because this people draw near with their mouth and honor me with their lips, while their hearts are far from me, and their fear of me is a commandment taught by men,

These verses also apply to Isaiah 29:13:

Matt 7:21 “Not everyone who says to me, ‘Lord, Lord,’ will enter the kingdom of heaven, but the one who does the will of my Father who is in heaven.

22 On that day many will say to me, ‘Lord, Lord, did we not prophesy in your name, and cast out demons in your name, and do many mighty works in your name?’

23 And then will I declare to them, ‘I never knew you; depart from me, you workers of lawlessness.’

James 2:19 You believe that God is one; you do well. Even the demons believe—and shudder!

The point is that lots of people think that Jesus is the Son of God. It does not mean that they really know Him. Rather, they know of Him, that He probably existed or even that He did exist, not much else, especially on the proper personal level.

@ Nelson (2nd comment):

III. TRINITY DOCTRINE

At this point I think its best to put forth the actual God, Jesus and the Holy Spirit's correct relationship as the Trinitarian concept is in fact incorrect as are other concepts concerning this matter. Perhaps we can then more easily see whats wrong with other beliefs. These things are hard to understand. The correct relationship is as follows:

Jesus is the Son of God, Lamb of God and King of kings=He has Deity as His Father has =we are to also worship Him but Jesus isn't His Father: The Trinity Doctrine (TD) is wrong (NOTE [for those told otherwise]: the word Bible doesn't affect interpretation-the TD does). Unfortunately, people CONFUSE TRUTH (this offends many)/HATE.

The TD claims there are 3 CO-EQUAL heads=1 God. However, if the 3 are not equal the TD does not and cannot apply - its null and void. Sadly, people use only a few verses and/or are not careful to read verses in whole Bible context. 1 Cor 4:6 =don't add or omit things from the Bible text:

The TD (as are other concepts) is a roadblock to true Bible interpretation (In part the Catholic church got the TD idea from Pagans. Others [ie. JWs, lds, islam, moonies and others] figured out the TD is in error but they did not know our true God, Son and Holy Spirit relationship)=they didn't know Jesus (as their claims indicate). They never rightly went to nor learned to trust and rightly follow Jesus. Who knows more about a house, the Builder or people whom moved in later?

1. JESUS:

Jesus is God's Son [His Word not God's Body {Christ's Spiritual Body =believers in Him} =John 1:1], equals the pure essence of God [He was and is not an angel as JWs claim -Heb 1:2-6] neitehr when in flesh nor in Heaven. Jesus was not replacing nor was He ever equal to His Father (see John 5:30; Phlp 2:6-7; Col 2:9). Jesus (His Spirit existed with God from before the universe existed) is the closest we get to know infinite God in flesh (only a vessel =God's 1st creation part -something like being God's voice-box -not just some created being as LDS and JWs believe) to deliver eternal truth in person -John 14:7 (stoops to our level so to speak).

Born of human woman (for His earthly mission), Jesus is a separate person-entity (He has His own soul [what makes a person an individual] and given a human body -and Mary ISN'T God's mother) but God gave Jesus authority to be treated as His Father (conceived of God's Holy Spirit =fullness of DEITY [He deserves worship -Matt 14:33; 28:9] -SIR-NAME God =Jesus' birthright, reward as God's Son and to sit at God's right hand). In conception, God and Mary gave part of each to Jesus' life.

To rightly know Jesus starts at John 1:1. W/o a language God couldn't reason, know His thoughts, create a universe, life nor talk to others. So Jn 1:1 names Jesus as God's language. Created in God's image, man has the same limits. Despite how primitive most organisms need language to function and live with others.

Your language (always part of you) can't usurp your authority, act on its own and never tells you what to do. Therefore, Jesus' claims are true (Jn 5:19,30; 8:28) -a student is never greater than his teacher. Your words pass understanding of you to your son. If your son learns all you teach him, he in effect becomes like/is you for all intents and purposes. For obeying you, you can reward him the highest position, your authority.

A father owns a business and teaches his son to run his business. He goes away and puts his son in charge, trusting he'll run it just as he would. If the son obeys and runs the business as the father did, in effect he's his father and can claim to be his father =like father, like son -while exactly like his father he's never equal to him even thoegh he has his father's authority. The same is true for God and His Son, whom fully did God's will not His own so His Father gave Him right to also be worshiped:

Rom 5:19 Adam's sin made many sinners but by Jesus' obedience many are to be righteous.

REF: Jn 12:49; 14:28-29; Lk 6:40; Col 1:15 -Jesus is in God's image by rightly obeying God; Heb 5:7-8; Lk 2:52 -Mk 13:32; 20:23; Phil 2:6; Jn 17; 15:1 =God NEVER BECAME His Son.

2. GOD:

Only one GOD can occupy infinity =God of Israel =no other legit gods exist (HE CAN'T DIE EVER and doesn't fit into an earthly body). God has ULTIMATE AUTHORITY Jesus and the Holy Spirit do not have. Only God knows the day and hour for the end -Mt 24:36 and appoints who sits with Him. God has a soul like us (makes Him an individual -ie. a cell nucleus only Spiritual). All 3 are 1 in Spirit [of God] but Jesus and the Holy Spirit submit fully to God. Being 1 doesn't apply to difference in authority =the TD does not apply.

As long as 1 true full 360 degrees (in all directions) infinity exists (which the Bible proves it exists) two or more full infinities cannot exist nor can two Gods occupy the same infinity. Only a Spirit can occupy true full infinity. Everything having physical properties is measurable. Infinity cannot be measured.

3. the HOLY SPIRIT:

The Holy Spirit is God's "Spiritual body" (God is Spirit -to be 100% pure the Holy Spirit [no form] MUST occupy true infinity (360 deg. in all directions) =no flaws, =always existed -you can move over or make a space within Yourself to create a univeerse separate from yourself and create borders & rules where you want them). The Holy Spirit acts on God's command:

Jn 16:13 When the Spirit of truth comes, he will guide you into all the truth, for he will not speak on his own authority, but whatever he hears he will speak, and he will declare to you the things that are to come.

God's body, voice & ears act on God's will -same for our body). The Holy Spirit can be called "He" (generic) as you can be called he(even if your ID is known). The Holy Spirit is more than deliverer of God's power, works and the word through Jesus (Jn 1:1-5; 4:23). Only the eternal truth, forever unchanged keeps God perfect =SEAMLESS Garment.

The point is many religious people started off with wrong beliefs, trusted in misinterpretations told to them along the way. Some started religions, often never double or triple checking what they thought was true or they allowed their desires and agendas or other influences to rule their decisions, some intentionally. Many well-meaning people were taken in along the way. Over many centuries many followed suit. Many zeroed in on few wrong things and made the mistake of not making the Bible an every day guide for correction of things overlooked by those around them. Will we do the same or will we check everything even if we thought some things were right up to now?

Many a religious organization will continue down wrong paths no matter what is told or shown to them. Some stay their course and perhaps patch a few things or even claim they have received new light or revelations but the wise will find the real path to Jesus. The point is the truth is complete within the Bible. Anything extra-Biblical regarding changing God's and Jesus' actual Biblical teaching is wrong by its very existence.

@ Nelson (3rd comment):

Again, because the Trinity Doctrine is wrong, it does not follow nor justify one making a whole new or different non-Biblical concept nor does it make them legitimate. Unfortunately for LDS, there are so many things that they believe and do that have nothing to do with actual Bible concepts, it makes LDS, in its entirety, false and fully beyond actual Biblical teaching.

The only way out of such a mess requires that those who want to follow our real God and Jesus get out of false religion and seek our real Jesus with all their heart and soul. Sadly, many will never do that, deciding not to step out of what has become a security and comfort zone for them (false though it is).

Jesus said, "Do not judge by appearances but judge with right judgment." (Jn 7:24). He did not say not to judge at all. The real Bible message is: Don't judge for wrong reasons nor judge to make yourself look better than another or for the purpose of lording it over others or for the sake of judging. There are those who will not make judgments simply because they do not want to upset the apple cart or buck the "status quo" but the wise want to learn the true purpose for what Jesus taught.

@ Daniel (4th comment):

Because someone's beliefs and claims are in part or in whole wrong does not mean they cannot see "holes" in another's beliefs or claims (and yes sometimes they may have their judgment wrong in whole or in part). It would be better if they would carefully examine their own beliefs to weed out what they got wrong from various sources but many won't. If one is wise, they won't allow themselves to get caught up in wrong teaching as they do not want to be mislead. Sadly, both the LDS and the JWs (and others) got so far away from what the Bible actually says I doubt that either would be willing to dump their entire teaching and start over. The same goes for many mainstream churches. Thanks for looking that verse up for me.

This is most definitely not the only reason that Jehovah's Witnesses and Mormons are often viewed as "non-Christian" but it is a major one. @metal had the right idea but it wouldn't let me comment on his post, so I am writing another answer instead. What some refer to as "Mainstream Christians" or "Mainstream Christianity" are usually inclusive of Catholic, Orthodox, Protestant, and Reformationist sects of Christianity (such as Baptist, Evangelical, Lutheran, Episcopalian, and others). These sects of Christianity are all tied together in their belief in the Ecumenical Christian Creeds, sometimes earning them the title "Creedal Christians". Restorationist Churches, such as the Jehovah's Witness and The Church of Jesus Christ of Latter-day Saints do not believe in these Creeds and since the creeds are such an integral part of the doctrinal tenets of "Mainstream Christianity", they are rejected as "Christians". Again, it is not the only reason, as everybody seems to have their own beliefs concerning the beliefs of these two churches, for good or bad (evidenced by the number of posts and comments of varying levels of contention and condemnation on this page). From a core doctrinal standpoint, however, the difference of belief in the Ecuminical Creeds is a very large point of conflict in their trying to claim their place within "Mainstream Christianity".

As a side note: I am a member of the LDS Church.

What is the basis that many mainstream Christian groups justify labeling groups like the Mormons and Jehovah’s Witnesses as Non Christians?

As far as Catholicism is concerned and possible some other denominations may be concerned neither the Mormons and Jehovah’s Witnesses is because the Church has declared their baptisms invalid and they do not believe in the Trinity as most mainstream Christian Churches understand this terminology.

Baptism makes us members of the Church! It is also the one sacrament that all true Christian denominations share in common: Catholics, Orthodox, Anglicans, Lutherans, and so on.

1213 Holy Baptism is the basis of the whole Christian life, the gateway to life in the Spirit (vitae spiritualis ianua),4 and the door which gives access to the other sacraments. Through Baptism we are freed from sin and reborn as sons of God; we become members of Christ, are incorporated into the Church and made sharers in her mission: "Baptism is the sacrament of regeneration through water in the word." - Catechism of the Catholic Church

In the eyes of the Catholic Church, any Baptism that uses water and the invocation of the Holy Trinity, as in “I baptize you in the name of the Father and of the Son and of the Holy Spirit,” is a valid sacrament. So if a follower of a Christian church that performs Baptism to these standards wants to become Catholic, he doesn’t have to be re-baptized. Also, the minister must intend to do what the Church does when baptizing.

Converts from the Mormon Church or from the Jehovah’s Witnesses must be rebaptized when entering into communion with the Catholic Church.

What the Early Church Believed: Trinitarian Baptism

For a sacrament to be valid, three things have to be present: the correct form, the correct matter, and the correct intention. With baptism, the correct intention is to do what the Church does, the correct matter is water, and the correct form is the baptizing “in the name of the Father and of the Son and of the Holy Spirit” (Matt. 28:19).

Unfortunately, not all religious organizations use this form. In fact, Jehovah’s Witnesses sometimes use no formula at all in their baptisms, and an even larger group, the “Jesus Only” Pentecostals, baptize “in the name of Jesus.” As a result, the baptisms of these groups are invalid; thus, they are not Christian, but pseudo-Christian.

Both groups also reject the Trinity. Jehovah’s Witnesses claim that Jesus is not God, a heresy known as Arianism (after its fourth-century founder), and the “Jesus Only” Pentecostals claim that there is only a single person, Jesus, in the Godhead, a heresy known as Sabellianism (after its inventor in the third century; see the Catholic Answers tract, God in Three Persons).

The early Church Fathers, of course, agreed. As the following quotes illustrate, Christians have from the beginning recognized that the correct form of baptism requires one to baptize “in the name of the Father and of the Son and of the Holy Spirit.”

The Didache

“After the foregoing instructions, baptize in the name of the Father, and of the Son, and of the Holy Spirit, in living [running] water. If you have no living water, then baptize in other water, and if you are not able in cold, then in warm. If you have neither, pour water three times on the head, in the name of the Father, and of the Son, and of the Holy Spirit. Before baptism, let the one baptizing and the one to be baptized fast, as also any others who are able” (Didache 7:1 [A.D. 70]).

In 2001, deemed that baptisms of the Church of Jesus Christ of the Latter-Day Saints were invalid, through a dubium posed by several American bishops.

The Question of the Validity Conferred in the Church of Jesus Christ of the Latter-Saints

The Congregation for the Doctrine of the Faith has given a negative response to a "Dubium" regarding the validity of Baptism conferred in the Church of Jesus Christ of Latter-day Saints, more commonly known as the Mormons. Given that this decision changes the past practice of not questioning the validity of such Baptism, it seems appropriate to explain the reasons that have led to this decision and to the resulting change of practice.

Doctrinal errors usually do not invalidate baptism

This explanation becomes even more necessary if one considers that errors of a doctrinal nature have never been considered sufficient to question the validity of the sacrament of Baptism. In fact, already in the middle of the third century Pope Stephen I, opposing the decisions of an African synod in 256 A.D., reaffirmed that the ancient practice of the imposition of hands as a sign of repentance should be maintained, but not the rebaptism of a heretic who enters the Catholic Church. In this way, the name of Christ attains great honour for faith and sanctification because whoever is baptized in the name of Christ, wherever that has taken place, has received the grace of Christ (cf. Denzinger-Hünermann [DH] 110-111). The same principle was upheld by the Synod of Arles in 314 (cf. DH 123). Well known also is the struggle of St Augustine against the Donatists. The Bishop of Hippo affirms that the validity of the sacrament depends neither on the personal sanctity of the minister nor on his belonging to the Church.

Right intention is the intention to do what the Church wants, what Christ wants

Even non-Catholics can validly administer Baptism. In every case, however, it is the Baptism of the Catholic Church, which does not belong to those who separate themselves from her but to the Church from which they have separated themselves (cf. Augustine, On Baptism 1, 12,9). This validity is possible because Christ is the true minister of the sacrament: Christ is the one who truly baptizes, whether it is Peter or Paul or Judas who baptizes (cf. Augustine, Treatise on the Gospel of John VI, 1,7; cf. CCC n. 1127). The Council of Trent, confirming this tradition, defined that Baptism administered by heretics in the name of the Father, the Son and the Holy Spirit, with the intention of doing what the Catholic Church does is true Baptism (cf. DH 1617).

The validity of doubtful baptism is presumed especially in the case of marriage, as in the case of the Christians of Nagasaki

The most recent documents of the Catholic Church maintain the same teaching. The Code of Canon Law prescribes that those who have been baptized in non-Catholic ecclesial communities (as long as there is no doubt regarding the matter or the form or the intention of the minister or of the person being baptized) should not be baptized again (cf. Code of Canon Law, can. 869 §2), Intrinsically connected to this problem is that of who can be the minister of Baptism in the Catholic Church. According to the Code, in cases of necessity anyone can baptize, provided the intention is correct (cf. can. 861 §2). The Code of Canon Law confirms the fundamental elements of Tridentine teaching and makes more explicit what is the required correct intention: "The intention required is to will to do what the Church does when she baptizes. The Church finds the reason for this possibility in the universal saving will of God and the necessity of Baptism for salvation" (CCC, n. 1256. Evidently, the necessity of Baptism spoken of here is not to be understood in an absolute sense; cf. ibid., nn. 1257-1261). Precisely because of the necessity of Baptism for salvation the Catholic Church has had the tendency of broadly recognizing this right intention in the conferring of this sacrament, even in the case of a false understanding of Trinitarian faith, as for example in the case of the Arians.

Taking into account this deeply-rooted practice of the Church, applied without any doubt as to the multiplicity of non-Catholic Christian communities emerging from the so-called Reform of the 16th century, it is easily understood that when there appeared in the United States the religious movement of Joseph Smith around 1830, in which the matter and the words of the form of Baptism were correctly utilized, this Baptism was considered valid, analogously to the Baptism of so many other non-Catholic ecclesial communities. Joseph Smith and Oliver Cowdery, according to their teaching, received the priesthood of Aaron in 1829. Given the circumstances of the Church in the United States in the 19th century and the means of social communication at that time, even though the new religious movement gained a considerable number of followers, the knowledge that ecclesiastical authorities could have had of the doctrinal errors that were professed in this new group was necessarily very limited throughout the entire century. For the practical cases that emerged there was applied the response of the Holy Office of 9 September 1868 given for the Christian communities of Japan which had remained isolated and without priests from the time of the persecution at the beginning of the 17th century. According to this response: 1) those persons about whom there was doubt whether they were validly baptized should be considered Christians; 2) this Baptism should be considered valid with regard to the validity of marriage (Gasparri, Fontes, IV, n. 1007).

Current doubts about the validity of Mormon baptism

In the 20th century, the Catholic Church became more aware of the Trinitarian errors which the teaching proposed by Smith contained, though he used the traditional terms, and therefore more and more doubts spread about the validity of the Baptism conferred by the Mormons, in spite of the fact that the form, as far as the substance of the terminology goes, coincided with that used by the Church. As a result, almost imperceptibly there developed difference of practice, insofar as those who had a certain personal knowledge of the teaching of the Mormons considered their Baptism invalid, while the common practice continued of applying the traditional principle of the presumption in favour of the validity of such Baptism, since there was no official norm in this regard. In recent years, as a result of a request from the Congregation for the Doctrine of the Faith, the Bishops' Conference of the United States undertook a detailed study of this delicate issue with the hope of coming to a definitive conclusion. On its part the Congregation for the Doctrine of the Faith undertook a new examination of the material that came from the United States and thus was able to resolve the proposed question.

What are the reasons which now led to this negative position regarding the Church of Jesus Christ of Latter-day Saints, which seems different from the position of the Catholic Church throughout the centuries?

Huge divergence on Trinity and baptism invalidates the intention of the Mormon minister of baptism and of the one to be baptized.

According to the traditional doctrine of the Catholic Church there are four requirements for the valid administration of the sacrament of Baptism: the matter, the form, the intention of the minister, and the right disposition of the recipient. Let us examine briefly each of these four elements in the teaching and practice of the Mormons.

I. The Matter. On this point there is no problem. Water is used. The Mormons practice Baptism by immersion (cf. Doctrine and Covenants [D&C] 20:74), which is one of the ways of celebrating Baptism (application of the matter) which is accepted by the Catholic Church.

II. The Form. We have seen that in the texts of the Magisterium on Baptism there is a reference to the invocation of the Trinity (to the sources already mentioned, the Fourth Lateran Council could be added here [DH 8021). The formula used by the Mormons might seem at first sight to be a Trinitarian formula. The text states: "Being commissioned by Jesus Christ, I baptize you in the name of the Father, and of the Son, and of the Holy Spirit" (cf. D&C 20:73). The similarities with the formula used by the Catholic Church are at first sight obvious, but in reality they are only apparent. There is not in fact a fundamental doctrinal agreement. There is not a true invocation of the Trinity because the Father, the Son and the Holy Spirit, according to the Church of Jesus Christ of Latter-day Saints, are not the three persons in which subsists the one Godhead, but three gods who form one divinity. One is different from the other, even though they exist in perfect harmony (Joseph F. Smith, ed., Teachings of the Prophet Joseph Smith [TPJSI, Salt Lake City: Desert Book, 1976, p. 372). The very word divinity has only a functional, not a substantial content, because the divinity originates when the three gods decided to unite and form the divinity to bring about human salvation (Encyclopaedia of Mormonism [EM], New York: Macmillan, 1992, cf. Vol. 2, p. 552). This divinity and man share the same nature and they are substantially equal. God the Father is an exalted man, native of another planet, who has acquired his divine status through a death similar to that of human beings, the necessary way to divinization (cf. TPJS, pp. 345-346). God the Father has relatives and this is explained by the doctrine of infinite regression of the gods who initially were mortal (cf. TPJS, p. 373). God the Father has a wife, the Heavenly Mother, with whom he shares the responsibility of creation. They procreate sons in the spiritual world. Their firstborn is Jesus Christ, equal to all men, who has acquired his divinity in a pre-mortal existence. Even the Holy Spirit is the son of heavenly parents. The Son and the Holy Spirit were procreated after the beginning of the creation of the world known to us (cf. EM, Vol. 2, p. 961). Four gods are directly responsible for the universe, three of whom have established a covenant and thus form the divinity.

As is easily seen, to the similarity of titles there does not correspond in any way a doctrinal content which can lead to the Christian doctrine of the Trinity. The words Father, Son and Holy Spirit, have for the Mormons a meaning totally different from the Christian meaning. The differences are so great that one cannot even consider that this doctrine is a heresy which emerged out of a false understanding of the Christian doctrine. The teaching of the Mormons has a completely different matrix. We do not find ourselves, therefore, before the case of the validity of Baptism administered by heretics, affirmed already from the first Christian centuries, nor of Baptism conferred in non-Catholic ecclesial communities, as noted in Canon 869 §2.

III. The Intention of the Celebrating Minister. Such doctrinal diversity, regarding the very notion of God, prevents the minister of the Church of Jesus Christ of Latter-day Saints from having the intention of doing what the Catholic Church does when she confers Baptism, that is, doing what Christ willed her to do when he instituted and mandated the sacrament of Baptism. This becomes even more evident when we consider that in their understanding Baptism was not instituted by Christ but by God and began with Adam (cf. Book of Moses 6:64). Christ simply commanded the practice of this rite; but this was not an innovation. It is clear that the intention of the Church in conferring Baptism is certainly to follow the mandate of Christ (cf. Mt 28,19) but at the same time to confer the sacrament that Christ had instituted. According to the New Testament, there is an essential difference between the Baptism of John and Christian Baptism. The Baptism of the Church of Jesus Christ of Latter-day Saints, which originated not in Christ but already at the beginning of creation (James E. Talmage, Articles of Faith [AF], Salt Lake City: Desert Book, 1990, cf. pp. 110-111), is not Christian Baptism; indeed, it denies its newness. The Mormon minister, who must necessarily be the "priest" (cf. D&C 20:38-58.107:13.14.20), therefore radically formed in their own doctrine, cannot have any other intention than that of doing what the Church of Jesus Christ of Latter-day Saints does, which is quite different in respect to what the Catholic Church intends to do when it baptizes, that is, the conferral of the sacrament of Baptism instituted by Christ, which means participation in his death and resurrection (cf. Rom 6,3-11; Col 2,12-13).

We can note two other differences, not as fundamental as the preceding one, but which also have their importance:

A) According to the Catholic Church, Baptism cancels not only personal sins but also original sin, and therefore even infants are baptized for the remission of sins (cf. the essential texts of the Council of Trent, DH 1513-1515). This remission of original sin is not accepted by the Church of Jesus Christ of Latter-day Saints, which denies the existence of this sin and therefore baptizes only persons who have the use of reason and are at least eight years old, excluding the mentally handicapped (cf. AF, pp. 113-116). In fact, the practice of the Catholic Church in conferring Baptism on infants is one of the main reasons for which the Mormons say that the Catholic Church apostatized in the first centuries, so that the sacraments celebrated by it are all invalid.

B) If a believer baptized in the Church of Jesus Christ of Latter-day Saints, after renouncing his or her faith or having been excommunicated, wants to return, he or she must be rebaptized (cf. AF, pp. 129-131).

Even in regard to these last elements it is clear that the Baptism of Mormons cannot be considered valid; since it is not Christian Baptism, the minister cannot have the intention of doing what the Catholic does.

IV. The Disposition of the Recipient. The person to be baptized, who already has the use of reason, has been instructed according to the very strict norms of the teaching and faith of the Church of Jesus Christ of Latter-day Saints. It must be maintained therefore that one cannot think that the Baptism received by that person is anything different from what he was taught. It does not seem possible that the person would have the same disposition that the Catholic Church requires for the Baptism of adults.

Difference of views: Mormons hold that there is no real Trinity, no original sin, that Christ did not institute baptism.

Summing up, we can say: The Baptism of the Catholic Church and that of the Church of Jesus Christ of Latter-day Saints differ essentially, both for what concerns faith in the Father, Son and Holy Spirit, in whose name Baptism is conferred, and for what concerns the relationship to Christ who instituted it. As a result of all this, it is understood that the Catholic Church has to consider invalid, that is to say, cannot consider true Baptism, the rite given that name by the Church of Jesus Christ of Latter-day Saints.

It is equally necessary to underline that the decision of the Congregation for the Doctrine of the Faith is a response to a particular question regarding the Baptism of Mormons and obviously does not indicate a judgment on those who are members of the Church of Jesus Christ of Latter-day Saints. Furthermore, Catholics and Mormons often find themselves working together on a range of problems regarding the common good of the entire human race. It can be hoped therefore that through further studies, dialogue and good will, there can be progress in reciprocal understanding and mutual respect.

Why do so many Christian religions claim The Church of Jesus Christ of Latter-day Saints (Mormons) are not Christian? was closed for being a duplicate of this question, but I didn't notice until my answer bounced. Rather than waste it, I've added a bit about JWs and am posting it here.

Consider Judaism and Christianity:

• Most Christian denominations believe that Christianity is an extension of Judaism.
• The Hebrew scriptures are accurate and true, but incomplete.
• The Greek scriptures complement and add new information to the Hebrew scriptures.
• Judaism rejects this added information as heresy.

Thus Christianity could be (and in its early days was) considered a part of Judaism, but not by Judaism.

Consider Christianity and Islam:

• Muslims believes that Islam is an extension of Christianity (and Judaism).
• The Hebrew and Greek scriptures were true, but only for the times and peoples they were written for.
• The Arabic scriptures not only provide additional information, they indicate which parts of the other scriptures were appropriate for their intended audience, but should not be considered true in the actual details.
• Christianity rejects this added information.

Thus Islam contradicts and negates part of Christianity, and so is heretical and cannot be considered as a Christian denomination, not even by Muslims.

Consider Christianity and Jehovah's Witnesses:

• Both believe that the Hebrew and Greek scriptures (the Bible) are the inspired word of God.
• Some mainstream Christians (e.g. Catholics) believe that there are other sources of truth (e.g. tradition and papal infallibility).
• Jehovah's Witnesses believe that most translations of the Bible contain significant errors, and in particular errors that were deliberately made in order to make the text conform to existing (false) Christian beliefs (e.g. the Trinity Doctrine).
• Most Christians believe that the Jehovah's Witnesses' New World Translation of the Bible contains significant errors, in particular errors that were deliberately made to make the text conform to (false) doctrine (e.g. Jesus was created by God).
• Each rejects some fundamental doctrines of the other, and each claims to be the one true Christian religion.

Thus each considers itself to be Christian, and each denies that the other is. JWs consider themselves to be Christianity, not to be part of Christianity.

Now consider Mormons:

• Mormons believe that the LDS Church is and extension of Christianity (and Judaism).
• The Hebrew and Greek scriptures are true, but incomplete, and are often misinterpreted by most of Christianity.
• The Book of Mormon provides additional information, without contradicting the Greek and Hebrew scriptures.
• Christianity rejects this added information, claiming it is man-made and uninspired, and that it does contradict the scriptures.

The conclusion here is not clear:

• If many Christians do misinterpret their own scriptures, which the Book of Mormon does not actually contradict, then just as with Judaism ⇒ Christianity, obviously the LDS Church is an extension of Christianity, and therefore still part of it.
• If the Book of Mormon actually does contradict the Greek and Hebrew scriptures, then the LDS church is not a continuation of the Christian Church.

The result is that Mormons justifiably consider themselves as Christians, while Christians justifiably reject this idea.

The main difference in situation is that while Mormons, JWs and mainstream Christianity each consider themselves to be true Christians, Mormons claim to have additional truth, while JWs claim to represent the original truth

Mainstream Christian groups limit the term 'Christian' to those who believe Jesus is the Christ and agree with them about what that means. The term 'Christian' isn't used for anyone who simply likes Jesus or believes he was special in some way. We can see this because Islam teaches that Jesus was a prophet, but Muslims aren't called 'Christian'! Similarly an atheist who thought Jesus was a good teacher wouldn't be called a Christian. Clearly it's more than just thinking highly of Jesus.

At the barest minimum, the term 'Christian' is used for people who believe that Jesus is the Christ, the Greek word for the Hebrew concept of the Messiah. The Messiah is a character prophesied about in the Old Testament, though there is much debate in and outside of Christianity as to what exactly it means to be the Messiah. Both mainstream Christian and restorationist groups such as the Mormons and Jehovah's Witnesses agree this far; they disagree, and limit how the term is used, because of what they believe the Messiah means.

What you call 'mainstream Christianity' is Trinitarian Christianity: they believe that the Messiah is God himself, who came incarnate to the earth. They call the other groups non-Christian because they believe the Jesus they proclaim actually has a very different identity. To Trinitarians saying that Jesus is a created being, is a 'mode' of God, or that he only became divine at his baptism is just as wrong as saying that God doesn't exist and Jesus was nothing more than a human teacher.

Trinitarian Christians believe their views are supported by the historical creeds, such as the Apostles' and Nicene creeds. When those creeds were first constructed there were many who disagreed with them, but by the time the first restorationist groups were founded the creeds were accepted by almost everyone; before the restorationist groups were founded 'Christian' and 'Trinitarian' were effectively synonymous.

Lastly, note that sometimes a group likes to reserve the label 'Christian' only for those who hold very similar beliefs to their own. You will find many protestants who will call the Roman Catholic Church a non-Christian organisation. They refuse to call the other side 'Christian' because they believe they have distorted the gospel or replaced it with a completely different gospel.

A fundamental issue here is that the term "Christian" admits different meanings. In a broad sense, a Christian is anyone who self-identifies as a follower of Jesus Christ (cf. Acts 11:26), which would include all bodies such as Catholics, Orthodox, Anglicans, Protestants, and Restorationists (including JWs and Mormons).

To use "Christian" in a narrower sense where some self-identified Christians are excluded, one needs to choose some criterion of orthodoxy by which to judge among groups. One common standard is the set of ecumenical creeds, which JWs and Mormons reject. Conversely, JWs reject trinitarians as genuine Christians for the opposite reason -- because they adhere to the ecumenical creeds, which JWs consider to be a blasphemous tradition, or because they reject the authority of the Governing Body of Jehovah's Witnesses. (Similar things could be said about Protestants and Catholics and the authority of the Pope and Tradition, though things have mellowed since Vatican II.)

As a specific example, in a debate from a few years back, evangelical Albert Mohler and Mormon Orson Scott Card went back and forth about whether Mormons are Christians. (The debate is hard to navigate, but it's all there; use the "previous" button at the bottom to get back to the beginning.) Mohler argues, in short, that Mormons don't hold to the ecumenical creeds about the nature of God and Christ, which the wide majority of Christians share, and are therefore not Christians, and Card responds by saying that Mormons are "non-traditional Christians," followers of Christ who reject the tradition embodied in the creeds.

Before we start to answer this, a little history is needed. Both the Latter-Day Saints and Jehovah's Witnesses are Restorationist churches. That means that they were founded on the belief that all the other churches in the world had ceased to hold to the whole correct Christian doctrine, and that a direct revelation from God to the founders caused them to start an entirely new church, and to separate themselves from the 'corrupt' churches that were then in existence (yes, 'corrupt' was the word they used at the time. I'm aware it has a technical meaning that isn't the same as 'dishonest', but it's not very polite even in its technical meaning, which is essentially of a church that has stopped following God). Today both will attempt to convert members of other denominations to their own faith, and insist that people baptized in other Christian denominations are rebaptized to become members of their sects. Cooperation of any kind between Mormons and mainstream churches is extremely rare (compared with cooperation between other denominations), and the non-mainstream sects are at least as assiduous in rejecting it as the mainstream churches.

So in short, both Mormons and JWs stated for themselves that they are a completely different faith from the mainstream church, and continue to act in that way towards others.

Mormons hold to an additional revelation and additional scriptures, belief in which they consider essential to their own faith, and which are not accepted by other churches and in many cases contradict the tenets of other churches. JWs use a unique Bible translation which they hold to be authoritative and which disagrees in many places with all other translations. Both hold to unique doctrines, particularly about the person of Jesus, which differ fundamentally from what mainstream churches believe and which they consider to be a non-negotiable part of their faith.

Given this, it is perhaps unsurprising that mainstream churches find it hard to accept churches which do not accept them as valid Christians. However this is by no means a fixed rule. Some denominations do accept Mormons and JWs as a valid form of Christianity.