Is it a sin or forbidden to follow any of the parts of the Law of Moses?

It depends on which part you are talking about. The Catholic position is that the Old Law ended and it is now unacceptable to follow its religious ceremonies, however, there are certain parts of the Old Law which are still in force, for example, "Thou shalt not steal" remains applicable.

Pope Eugene IV, Council of Florence, 1441,
“The Holy Roman Church firmly believes, professes and teaches that the matter pertaining to the law of the Old Testament, the Mosaic law, which are divided into ceremonies, sacred rites, sacrifices, and sacraments… after our Lord’s coming… ceased, and the sacraments of the New Testament began... All, therefore, who after that time (the promulgation of the Gospel) observe circumcision and the Sabbath and the other requirements of the law, the holy Roman Church declares alien to the Christian faith and not in the least fit to participate in eternal salvation.

You can still follow the old law, but the condition is still the same: everything is applicable. If you fail in one, you have sinned. The stoners were guilty in the moral realm (adultery) if they commited even a minor infraction in the ceremonial! I recommend you read Deuteronomy 28-30.

James 2:10 NET For the one who obeys the whole law but fails in one point has become guilty of all of it.

Background to the Mosaic Law

The Purpose of the Law

The law was given to make Israel God's People, Abraham's Seed, and to bless the world, to bring it back to God, reverse the expulsion from Eden.

Method

Israel needed to:

Obey the law

Receive blessings

Impress the surrounding nations

Achievement, success rate

Rahab turned to God on seeing the victories given to Israel.

Why were the achievements so few?

Because the observance of law was so insignificant.

Because the law itself was an inferior covenant

Even if the people depended on God, and took possession of the land, the pagan nations who were impressed and converted to Judaism would find forgiveness, but not empowerment, ability to live the eternal life, chayei olam. Moses quickly realised that this was an inferior glory, but did not want to dishearten the people. He covered his face with a veil so that the people would not be demoralised at seeing the glowing radiance fade from his face. They had just left Egypt, were wanderers in the wilderness and needed all the hope and encouragement they could get. Telling them that full redemption was a future event was not exactly the message they needed to hear.

When Jesus fulfilled the law, He won the rewards associated with Sinaitic Law. God blessed His Nation when Jesus, representing its people, Israel, obeyed the law.

To be pure, the citizen needed to make the right choices with regard to the natural drives of his body: harvesting the fruits of your own land was good, those from your neighbours land, bad. Sex with your wife was good, with your neighbour's wife, bad. The appetites themsrlves, yetzer hara, were themselves not bad, only the wrong exercising of those appetites. Man, made in the image of God, with a moral compass, could differentiate and choose, unlike wild beasts. Hence the concept of justice, as opposed to the law of the jungle, might is right.

Mercy and love are also what characterize the human race. Only humans do not destroy the weak in their family. They lay down their lives (categorised by the various acts of sacrificing one's own reserve food, shelter and resources, to protect the weak) .

In order to be the people and the nation God required, Israel found it had to have a right mind and a right body. The mind had to be subdued, by accepting the word of God, and the body had to be broken, to serve the mind, just as a horse needed to be subdued, to be useful for riding. The right mindset in the right body could create the right people in the right nation.

Joshua could not give Israel closure, only God could. The virgin birth proved that. Just as Isaac was possible because of an ovum provided by God (Sarah's womb was as good as dead) and his birth proof of God's causation, Jesus was proof that it was God who provided the Lamb, from a spermatozoon supernaturaly produced and implanted.

The blood of Jesus could do what no blood of bulls and goats did. It cleansed Israel and it cleansed her Temple. It cleansed the mind of those who agreed with the Gospel (here was the Messiah who vindicated the righteous and reconciled them with God, and who could redeem them, both their minds and their bodies, through confession : con>with, fess>speech, agreement) . If you were righteous, you could be vindicated; if you were unrighteous, you could repent and then be reconciled.

Now, the Church is to be a pure people in a pure community, its members to have a pure mind in a pure body. An obedient church could now act out that righteousness:

Romans 7:24-25 NET Wretched man that I am! Who will rescue me from this body of death? Thanks be to God through Jesus Christ our Lord! So then, I myself serve the law of God with my mind, but with my flesh I serve the law of sin.

Original Question

Are there some cases where it is sinful or forbidden to follow any of the laws in the Old Testament, now that Jesus has fulfilled these laws (Romans 10:4; Galatians 3:23-25; Ephesians 2:15)?

Now that the church enjoys the blessings meant for God's People, what remains of the law? Since Jesus won redemption for the church through obedience to the law, obedience to the law now wins redemption for the world:

Colossians 1:24 NET Now I rejoice in my sufferings for you, and I fill up in my physical body – for the sake of his body, the church – what is lacking in the sufferings of Christ.

The form in which you follow law could be the Mosaic law, which requires ALL requirements to be fulfilled, or you could follow the law of liberty and love, the Royal Law, requiring holy living, enabling God to use one for ministry.

2 Timothy 2:20-21 NET Now in a wealthy home there are not only gold and silver vessels, but also ones made of wood and of clay, and some are for honorable use, but others for ignoble use. So if someone cleanses himself of such behavior, he will be a vessel for honorable use, set apart, useful for the Master, prepared for every good work.

Following the Mosaic Law is not sin. Its just impossible, since ALL requirements cannot be met, leading to death, impotency. No benefit is achieved. Mosaic Law observed through faith provides only guardianship care, which is already a obsolete, redundant in the Gospel, which provides restoration and empowerment of the prodigal. However, however, it is better to misunderstand the Gospel in seeing the continued necessity of Mosaic Law as a lifestyle, not as salvific, than to misunderstand the Gospel by viewing the requirement of the new, Royal Law to be mental assent to the message that Jesus is the Messiah, the Holy One of God (Free Grace Theology) leading to the gift of immortality.

Would the Jews have been sinners in obeying Law in stoning the adulteress? Talmudic interpretation makes a right call in its interpretation of Torah. There, even lex talionis, eye for an eye, calls for monetary compensation for accidental bodily injury of another person, and even in that, mercy could be shown to those unable to pay.

It boils down to interpretation:

Mark 2:27 NET Then he said to them, “The Sabbath was made for people, not people for the Sabbath.

How is the law made for man, and not man for the law?

It was supposed to give life!

Romans 7:10 NET and I died. So I found that the very commandment that was intended to bring life brought death!

Hillel "Whatever is hateful to you, do not do unto another. That is the whole of the Torah. The rest is commentary."

Human degree of consciousness applied in historical context decides if a law is good or not. The laws of Moses were useful, in the context when laws and understanding weren't serve the life at that time. The Hebrews infected with idolatry disease taken after long stay with Egyptians, saw the big miracles applied by Moses to punish the oppressors, they went on dry through the middle of the splitted Red sea, and they saw lots other miracles during journey in desert. Still having the same eyes and same minds they considered that a golden calf made by their hands was their saviour against egyption threat. Of course, nowadays is inconceivable for our modern minds to embrace this kind of illusory.

Why?

Because God cured and taught us, in the meantime. The humanity consciousness evolved along history. 2000 years ago, the most civilized cultures, Greek and Roman, still have gods for everything: gods for hunting, gods for fertility, good for food, for wine, for seas, for beauty, for trade ...

How disappeared all these in less than 300 years?

God stated on earth, born as a simple human, he passed all ages from childhood to maturity going through temptations of the sinful nature of human body in all critical ages. Defeating all possible sins that a human can do, he start to teach us with simple words using simple parables, explaining what is good, and what wrong, what is sin and what is virtue, where the sins came from. He make a "fire" on Golgotha, a "fire" of a new understanding, a new wisdom. He sent his witnesses to spread this "fire" through the entire world. Many martirs paid with their blood, and many askets, monarchs, devoutly people has kept His "fire" burning until nowadays

Would has been possible to receive this new level of wisdom without to experience the laws of Moses?

I think not. Because the laws of Moses served as a unit of measures for our sins. Without having this unit of measure, his words like: "You have heard that it was said to the people long ago ..." (Matthew 5) would not be possible.

When He stopped the furious crowd to stone the adulteress till death, He wrote in a dust of human heart a new law brought from His Kingdom, unknown from Moses laws: HUMILITY. He point our view from outside to inside, from other's sins to our own sins.

He didn't forced our understanding, imposing this new law as an almighty God. He appeal to our will as rational beings, respecting our freedom to choose between good and evil. We are free today to think what we want about his pronia, to judge Him, to see Him as a killer god, to reject Him, or to see His overwhelming love for human nature.

The Old Testament centered of Laws of Moses is not only a historic record of humanity. Is in the same time history of thoughts to the soul of any human.

Matthew 5:17 states that we still need the law----

17 Don’t misunderstand why I have come. I did not come to abolish the law of Moses or the writings of the prophets. No, I came to accomplish their purpose. 18 I tell you the truth, until heaven and earth disappear, not even the smallest detail of God’s law will disappear until its purpose is achieved.

According to this verse, the law is required and it’s a very important part of what God is trying to achieve. Therefore, we should wholeheartedly try to determine what role the law plays in our salvation. Verse 19 may give us part of the answer

Matthew 5:19
Whosoever therefore shall break one of these least commandments and shall teach men so, he shall be called the least in the Kingdom of Heaven; but whosoever shall do and teach them, the same shall be called great in the Kingdom of Heaven.

After reading this verse, it appears that you do not have to follow the Law in order to go to heaven; it just determines if you are the least or the greatest in the Kingdom of Heaven.

1 Corinthians 3:11-15 talks about the foundation of Jesus Christ, and that the materials "WE" choose, for building on that foundation, will be tested by the fire of judgement.

1 Corinthians 3:15

But if the work is burned up, the builder will suffer great loss. The builder will be saved, but like someone barely escaping through a wall of flames.

With these verses, it seems pretty clear that all we need in order to be saved, and to enter the Kingdom of Heaven is a belief in Jesus Christ. But, they also indicate that the kind of relationship you have with Jesus is also very important.

Be careful about spending too much time and energy trying to figure out where the line is, between good and evil. Instead

Abstain from all appearance of evil. (1 Thessalonians 5:22)

Think about your earthly relationships, marriage, friendship, co-workers, boss, family.

1. What would happen to those relationships if you kept trying to figure out where the line was?

2. What is the minimum that I have to do, in order to maintain this relationship?

   You may not actually say that out loud, or even consciously think it, but what if that was the way you conducted yourself? In the process of trying to figure out where the line is, you would inevitably cross it once or twice (or more). And then, once you felt that you had a pretty good idea of where that line was, would you spend all of your time (or most of your time) living near that line? And again, if you did spend most of your time living along that line, isn’t it likely that you would accidentally cross it every once in a while?

You’ve heard the phrase, “Marriage is 50/50”. That was said amongst a group of people once, and an elderly lady spoke up and said, “No, it’s 100/100”.
Interesting thought.

Think about those two types of marriage. Which one would be more stable, intimate, and fulfilling? Which one would be more likely to withstand conflict, stress, tragedy? Apply those thoughts to your other relationships.
Which one is more likely to feel as though you just escaped through a wall of flames?

Now, apply the above to your relationship with Jesus.

I think it’s safe to say that Jesus has committed 100% to the relationship. I think it’s also safe to say that no one is capable of giving 100% back "for all have fallen short" (Romans 3:23). But wouldn’t you rather be closer to the 100%, than to the wall of flames? Wouldn’t you rather be closer to the greatest, than to the least? Wouldn’t you rather be closer to Jesus?

God's love and grace is ever present and always available. In order for us to be made right by this: --We must accept Christ as our Lord and Savior (Romans 10:9)
--Believe in the foundation of Jesus Christ (John 5:24 --- Romans 3:25)
--Do it with a sincere and submissive heart (Luke 10:27-28 --- Romans 10:10).
--In doing so, we will grow in a relationship with Christ and the Holy Spirit (Colossians 2:6-7 … 1 John 4:17).
--This relationship will produce a desire to love and serve the Lord (Deuteronomy 10:12 -- Romans 2:29).
--An important part of this relationship is the Holy Spirit (Romans 8:9). We are instructed to follow the Holy Spirit (Galatians 5:25), who will help us fight the desires of our sinful nature (Galatians 5:16).
--And as this relationship grows, we will have a growing desire to follow God’s perfect law (Romans 7:12 --- James 1:27), in order to please the Lord (1 John 2:3-6; 1 John 5:3)
--In our own efforts to follow the law…we will fail and fall short (Romans 3:23).
The only way to fulfill the requirements of the law, is to follow the Holy Spirit (Romans 8:4).

Galatians 5:5

BUT WE who live by the Spirit EAGERLY WAIT TO RECEIVE by faith THE RIGHTEOUSNESS THAT GOD HAS PROMISED US.
(If we read only the capitol letters then all we have to do is wait)

During this whole messy process, God will examine our hearts and judge accordingly (Jerimiah 17:10; Ezk 18:30 ;1 Corinthians 3:11-15).
And if our heart is not in relationship with the Lord. He will say---(NLT)
“I never knew you. Get away from me, you who break God’s laws.” (Matthew 7:23).

The sin in your life is something that is beyond your control but that does not mean that you go on living in that sin (Romans 6:15). God has given us tools to help fight against that sin (Romans 6:17-22). As you recognize the sin in your life (and that recognition is accomplished by God’s law (Romans 7:7 --- Romans 3:20) plead with the Holy Spirit to help you turn from that sin (Psalm 143:10).

(Romans 7:24-25)

24 Oh, what a miserable person I am! Who will free me from this life that is dominated by sin and death? 25 Thank God! The answer is in Jesus Christ our Lord.

Again, I think we can all agree that a belief and faith in Jesus Christ is the answer. But I want to encourage everyone to think about what that means, and to think about it with a sincere and submissive heart. Most translations of Ecclesiastes 1:16 start off with

....I said to myself.

But I love the older translations

... I communed with mine own heart

In Matt 5:17 Christ is recorded as saying: "Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfill them.

A second point to consider is that of the idea of dispensationalism, which (in a very brief nutshell) is the idea that we (humans) have lived under different dispensations or covenant styles of God's relationship with man - for example: there was one mode of His dealing with and interacting with mankind prior to Christ's resurrection, and upon the salvation offered to us through his Sacrifice (taking on our sin), a new order or dispensation was established (that noted of salvation and forgiveness), and upon the time at the end of the age and the beginning of the time of the New Jerusalem (see Revelation), there will be yet a third dispensation (relationship style).

That said, as humans, we have been given The Law (of the Old Testament: see Exodus and Deuteronomy for examples) and nowhere in the New Testament Scriptures are we instructed to now simply forgo respecting those old Laws. Paul mentions that it is by The Law that we humans come to know and understand our own actions as being sinful or in-line with God's will - so through the Law, we can recognize our failures and recognize sin in our own hearts.

Also recall, that in the Garden of Eden, Adam and Eve were instructed not to eat of the tree of the “knowledge of good and evil.” Prior to enjoying this ‘apple’ they we are told that they were naked and that they were not ashamed of this fact – i.e. they did not even know to consider if they should be ashamed or not of their nakedness – they were without the understanding of there being anything about good and evil. There was only God and the garden in which they lived with God. When they took of the fruit, they were misbehaving, yes, but in that act they became aware of and knowledgeable of good and evil – and they then started to realize all that was either good or evil in their own existence and ways – their nakedness for instance.

One has to be aware of what is good and what is evil before he can elect to even try to forgo what is evil and follow what is good. A newborn may act in a selfish manner, but he is no more able to even consider his actions as good or evil, right or wrong, than he could drive a car and know to keep tot eh speed limit. He is not aware yet of what he is doing could even be wrong or right, (evil or good). He initially learns these things according to what he is taught within his home as being right and wrong, and later to a greater degree within the culture he elects to respect.

This brings us to the question (as per the topic point here) as to if Christians are supposed to continue to follow the old Mosaic Laws; and I will place two different law 'types' for an example here, to show that we are:

The laws regarding burnt offerings (which clearly no Christian denomination is advocating the continuation of burning animals as sacrifices to God). There are numerous Old Testament Laws going through nuance after nuance of how and why to make various burnt sacrifices to God depending upon the situation at hand. These sacrifices were performed as a means of atoning for one’s sins (breaking of the law). When Christ came though, He took on all mankind’s sins (passed present and future) and became the sacrificial lamb for all when he was sacrificed on the cross. Upon his resurrection, a new dispensation, a new covenant started, and although the old rules remained, there was now no need for anyone to put forth a burnt offering for their atonement, of breaking the laws, for Christ had already paid that fine, that debt. De we then, or are we supposed to stone someone for adultery, as the Law stated in the Old Testament? No. Why not? Would that not then be denying the Law? It would, if it were not that Christ has already paid the fine for that person’s sin – he has already died for that sin. Does this mean that we are free to sin then? “May it never be …” (see Romans) for each time we sin, we are in a sense driving a nail into Christ’s hands and feet, and we injure ourselves, for in that sin, we are not embracing the relationship with God, which we are otherwise offered to simply accept, if we would act properly. But even here, we have a way to be redeemed to that relationship when we repent of the sin, and accept Christ’s death as the ransom for our own sins. In this way too, we are not to condemn another for their sins, but to point the sin out (in love), and help him repent (see the law of what is right and wrong) ask for forgiveness, and accept the Grace of God as offered to each of us, if – again- we would simply accept Christ as our Savior…and move on to (try and) sin no more.

Christ also pointed out to us, that the physical action of breaking a Law, was not necessarily the only way to break the Law, for the law can be broken in the heart of man, though he elect not to act upon his sin of the heart (ex: Matt 5:28).

That Christ forgave the woman, did not equate to Christ saying that the Law was no longer relevant, but rather what the punishment would be, and who should rightfully be doling out that punishment were placed in a new light of His sacrifice (which he was about to undergo) - Him fulfilling the Law and the prophecies, and now taking on our sin (i.e. the woman's as well), and her sin now forgiven (recall he told her sin was forgiven and to go and sin no more), for he did not condemn her.

So...it is not a sin to follow the old Laws, in fact, we are to follow them. But whereas in the old dispensation, the old time, prior to Christ, the "fine" was to be done by the people (stone someone, or give a burnt offering), in the light of Christ being the sacrifice for all the sins we (or others) do, the aspect of who is in charge of doling out the fine of breaking the Law is now back in the hands of God, and no longer in ours. see Matt 22:40 for a summary of all the law.

Many scholars question the authenticity of the Pericope Adulterae (the section of scripture you cited in the original post).

http://bible.org/article/my-favorite-passage-that%E2%80%99s-not-bible

Professor Daniel Wallace writes,

For a long time, biblical scholars have recognized the poor textual credentials of the story of the woman caught in adultery (John 7:53–8:11). The evidence against its authenticity is overwhelming: The earliest manuscripts with substantial portions of John’s Gospel (P66 and P75) lack these verses. They skip from John 7:52 to 8:12. The oldest large codices of the Bible also lack these verses: codex Sinaiticus and Vaticanus, both from the fourth century, are normally considered to be the most important biblical manuscripts of the NT extant today. Neither of them has these verses. Codex Alexandrinus, from the fifth century, lacks several leaves in the middle of John. But because of the consistency of the letter size, width of lines, and lines per page, the evidence is conclusive that this manuscript also lacked the pericope adulterae. Codex Ephraemi Rescriptus, also from the fifth century, apparently lacked these verses as well (it is similar to Alexandrinus in that some leaves are missing). The earliest extant manuscript to have these verses is codex Bezae, an eccentric text once in the possession of Theodore Beza. He gave this manuscript to the University of Cambridge in 1581 as a gift, telling the school that he was confident that the scholars there would be able to figure out its significance. He washed his hands of the document. Bezae is indeed the most eccentric NT manuscript extant today, yet it is the chief representative of the Western text-type (the text-form that became dominant in Rome and the Latin West).

When P66, P75, Sinaiticus, and Vaticanus agree, their combined testimony is overwhelmingly strong that a particular reading is not authentic. But it is not only the early Greek manuscripts that lack this text. The great majority of Greek manuscripts through the first eight centuries lack this pericope. And except for Bezae (or codex D), virtually all of the most important Greek witnesses through the first eight centuries do not have the verses. Of the three most important early versions of the New Testament (Coptic, Latin, Syriac), two of them lack the story in their earliest and best witnesses. The Latin alone has the story in its best early witnesses.

Even patristic writers seemed to overlook this text. Bruce Metzger, arguably the greatest textual critic of the twentieth century, argued that “No Greek Church Father prior to Euthymius Zigabenus (twelfth century) comments on the passage, and Euthymius declares that the accurate copies of the Gospel do not contain it” (Textual Commentary, 2nd ed., loc. cit.).

Simply put, you're establishing a theological concept on a particular passage of the Bible which may not have even been in the original manuscripts.