Apart from any claim related to antiquity, does the modern Roman Catholic Church claim to be ‘The Body of Christ'?

Paul states in 1 Corinthians 12:12-27 that the church is one body, with many parts. The one body being the body of Christ. This is also stated in Romans 12:4-5, again by Paul. Paul outright says the Church is Christ's body in Colossians 1:24. Back in the day, when there was one universal "catholic"(as opposed to Roman Catholic ), there was one church, thus that Church was the Universal body of Christ. The Catholic church . They, themselves say this in their Catechism shown here, via google cache. Pope Francis, back in 2013 also proclaimed that the church was Christs's body as well

Among other answers, which I will try to provide as time permits, one answer as to why the Roman Catholic Church considers herself to be the valid church is its fruit; that is, its 1.3 billion members.

In turn, this idea sources back to Clement of Rome's First Epistle to the Corinthians in which he states the following (bold mine).

For, when rivalry arose concerning the priesthood, and the tribes were contending among themselves as to which of them should be adorned with that glorious title, he [Moses] commanded the twelve princes of the tribes to bring him their rods, each one being inscribed with the name of the tribe. ... And the rod of Aaron was found not only to have blossomed, but to bear fruit upon it.

Thus, when one considers which Church is the valid Church, one should consider the Church that not only has blossomed, but has also born fruit through the centuries.

The Papacy.

St Ambrose in the fourth century said:

Ubi Petrus ibi ergo Ecclesia

which means

Where Peter is, there, consequently, is the Church.

The Church of Rome believes a) Jesus entrusted to St. Peter primacy over the other apostles and b) that St Peter became the first Bishop of Rome and c) that subsequent Bishops of Rome have inherited that primacy.

The passage in which Peter was appointed is Matthew 16 verses 15 to 19.

(Jesus) saith unto them, But whom say ye that I am? And Simon Peter answered and said, Thou art the Christ, the Son of the living God. And Jesus answered and said unto him, Blessed art thou, Simon Barjona: for flesh and blood hath not revealed it unto thee, but my Father which is in heaven. And I say also unto thee, That thou art Peter, and upon this rock I will build my church; and the gates of hell shall not prevail against it. And I will give unto thee the keys of the kingdom of heaven: and whatsoever thou shalt bind on earth shall be bound in heaven: and whatsoever thou shalt loose on earth shall be loosed in heaven.

Peter was frequently the spokesperson, and received the commission to "Feed my sheep" (John 21). He preached the sermon on the first Whit Sunday (Acts 2) and it was to Peter that the revelation that Christianity was also for Gentiles was given (Acts 10).

The Church of Rome believes in Papal Infallibility (although in very limited circumstances).

There is a section of the Catechism of the Catholic Church entitled "Who belongs to the Catholic Church?" Paragraph 837 declares:

Fully incorporated into the society of the Church are those who, possessing the Spirit of Christ, accept all the means of salvation given to the Church together with her entire organization, and who - by the bonds constituted by the profession of faith, the sacraments, ecclesiastical government, and communion - are joined in the visible structure of the Church of Christ, who rules her through the Supreme Pontiff and the bishops

The special claim of the Roman Catholic Church, whether Latin Rite or Eastern Catholic, is its unity with the Supreme Pontiff, the Roman Pope.

Paragraph 838 goes on:

The Church knows that she is joined in many ways to the baptized who are honoured by the name of Christian, but do not profess the Catholic faith in its entirety or have not preserved unity or communion under the successor of Peter."

Here again it is union with the successor of Peter that uniquely defines Roman Catholicism.

The special status claimed for the Roman Catholic Church, however articulated, derives from the doctrinal belief that the Roman Papacy is a divinely appointed institution.

Besides antiquity, and continuity, the Roman Catholic Claims of being the Universal Church is also under-girded by an ancient Ecclesiology that is found in scripture, namely that "the Church is One". When you take this principle together with the notions of antiquity and continuity you have something of a three fold knot (Ecclesiastes 4:12).

There are many scriptures that speak to the idea that the Church as intended by Christ, or idealy speaking is one body. Here are a few of the best ones:

John 17: 20 “My prayer is not for them alone. I pray also for those who will believe in me through their message, 21 that all of them may be one, Father, just as you are in me and I am in you. May they also be in us so that the world may believe that you have sent me.

1 Corinthians 12: 12 "The body is a unit, though it is comprised of many parts. And although its parts are many, they all form one body. So it is with Christ."

Ephesians 2:21 "In Him the whole building is fitted together and grows into a holy temple in the Lord."

Romans 12:5 "so we, who are many, are one body in Christ, and individually members one of another."

Besides this there is a principle known as the "Canon of Saint Vincent" that is widely regarded by Churches of Apostolic Succession as a way of describing a criterion Holy Tradition. The Canon says, "Moreover, in the Catholic Church itself, all possible care must be taken, that we hold that faith which has been believed everywhere, always, by all". Theologians who use this canon, look for consensus among the Church Fathers for finding authoritative teaching, and on that subject, it easy to find a consensus with the Early Fathers on this subject.

Clement of Rome:

Accept our counsel and you will have nothing to regret. . . . If anyone disobeys the things which have been said by him [Jesus] through us, let them know that they will involve themselves in no small danger. We, however, shall be innocent of this sin and will pray with entreaty and supplication that the Creator of all may keep unharmed the number of his elect (Letter to the Corinthians 58:2, 59:1[A.D. 95]).

Ignatius of Antioch:

You [the See of Rome] have envied no one, but others have you taught. I desire only that what you have enjoined in your instructions may remain in force (Epistle to the Romans 3:1 [A.D. 110]).

Irenaeus:

But since it would be too long to enumerate in such a volume as this the succession of all the churches, we shall confound all those who, in whatever manner, whether through self-satisfaction or vainglory, or through blindness and wicked opinion, assemble other than where it is proper, by pointing out here the successions of the bishops of the greatest and most ancient church known to all, founded and organized at Rome by the two most glorious apostles. Peter and Paul, that church which has the tradition and the faith which comes down to us after having been announced to men by the apostles. With that church, because of its superior origin, all the churches must agree, that is, all the faithful in the whole world, and it is in her that the faithful everywhere have maintained the apostolic tradition (Against Heresies 3:3:2 [inter A.D. 189]).

Clement of Alexandria:

[T]he blessed Peter, the chosen, the preeminent, the first among the disciples, for whom alone with himself the Savior paid the tribute [Matt. 17:27], quickly grasped and understood their meaning. And what does he say? “Behold, we have left all and have followed you” [Matt. 19:2 7, Mark 10:28] (Who is the Rich Man that is Saved? 21:3-5 [A.D. 200]).

Tertullian:

[T]he Lord said to Peter, “On this rock I will build my Church, I have given you the keys of the kingdom of heaven [and] whatever you shall have bound or loosed on earth will be bound or loosed in heaven” [Matt. 16:18-19]. ... Upon you, he says, I will build my Church; and I will give to you the keys, not to the Church; and whatever you shall have bound or you shall have loosed, not what they shall have bound or they shall have loosed (Modesty 21:9-10 [A.D. 220]).

Letter of Clement to James:

Be it known to you, my lord, that Simon [Peter], who, for the sake of the true faith, and the most sure foundation of his doctrine, was set apart to be the foundation of the Church, and for this end was by Jesus himself, with his truthful mouth, named Peter, the first-fruits of our Lord, the first of the apostles; to whom first the Father revealed the Son; whom the Christ, with good reason, blessed; the called, and elect (Letter of Clement to James 2 [A.D, 221]).

Origen:

And Peter, on whom the Church of Christ is built, against which the gates of hell shall not prevail left only one epistle of acknowledged genuineness (Commentaries on John 5:3 [A.D. 226-232]).

Cyprian:

With a false bishop appointed for themselves by heretics, they dare even to set sail and carry letters from schismatics and blasphemers to the Chair of Peter and to the principal church [at Rome], in which sacerdotal unity has its source" (Epistle to Cornelius [Bishop of Rome] 59:14 [A.D. 252]).

Constantine Augustus:

and that the opposing parties who were contending persistently and incessantly with each other, should be summoned from Africa; that in their presence, and in the presence of the bishop of Rome, the matter which appeared to be causing the disturbance might be examined and decided with all care (To Chrestus [A.D. 314] as recorded by Eusebius).

Cyril of Jerusalem:

In the power of the same Holy Spirit, Peter, both the chief of the apostles and the keeper of the keys of the kingdom of heaven, in the name of Christ healed Aeneas the paralytic at Lydda, which is now called Diospolis [Acts 9 ;3 2-3 4] (Catechetical Lectures 17;27 [A.D. 350]).

Optatus:

In the city of Rome the Episcopal chair was given first to Peter, the chair in which Peter sat, the same who was head — that is why he is also called Cephas — of all the apostles, the one chair in which unity is maintained by all. Neither do the apostles proceed individually on their own, and anyone who would [presume to] set up another chair in opposition to that single chair would, by that very fact, be a schismatic and a sinner. . . . Recall, then, the origins of your chair, those of you who wish to claim for yourselves the title of holy Church" (The Schism of the Donatists 2:2 [circa A.D. 367]).

Ephraim:

Simon, my follower, I have made you the foundation of the holy Church. I betimes called you Peter, because you will support all its tall buildings. You are the inspector of those who will build on earth a Church for Me. If they should wish to build what is false, you, the foundation, will condemn them. You are the head of the fountain from which my teaching flows, you are the chief of my disciples. Through you I will give drink to all peoples (Homilies 4:1 [inter A.D. 338-373]).

Ambrose of Milan:

[Christ] made answer: “You are Peter, and upon this rock will I build my Church . . .” Could he not, then, strengthen the faith of the man to whom, acting on his own authority, he gave the kingdom, whom he called the rock, thereby declaring him to be the foundation of the Church [Matt. 16:18]? (The Faith 4:5 [A.D. 379]).

Tyrannius Rufinus:

and further how he speaks of the city of Rome, which now through the grace of God is reckoned by Christians as their capital (Apology 2:23 [A.D. 400])

Augustine:

Among these [apostles] Peter alone almost everywhere deserved to represent the whole Church. Because of that representation of the Church, which only he bore, he deserved to hear “I will give to you the keys of the kingdom of heaven" (Sermons 295:2 [A.D. 411]).

Taken from The Early Church Fathers on the Primacy of Peter / Rome.

The question itself is inherently flawed, for several reasons (and thus any attempt at an answer is thus fallacious and mistaken):

Off the top of my head:

• Any claim to be the true Church outside of demonstrating it historically amounts at best to 'good persuasion' (yes, as subjective as it sounds) to your personal (i.e., not historical) interpretation of Scripture, which is nothing objective and meaningless as a standard for determining which Church Christ founded. (You don't get to simply say, 'but, but it does mean this.' No one should have to simply accept that your interpretation is the final and correct one, which they need to in order to know that they've happened upon the Church, not a potential 'the Church.'

  As St. Athanasius points out, the only difference between an Arius and an Athanasius is "how many Fathers [of the Church] can you cite for your [beliefs]?" It does no good to argue from Scripture, because both sides did, and lots.

• You cannot use the Bible to prove you are the true Church alone (i.e. as excluding the argument from ancientness/originality/apostolicity), either, since, historically speaking (the history can't be ignored simply because history specifically isn't the criterion in view), it was what everyone would have to call the Catholic Church that codified what constitutes the Bible before which time there were disagreements about what constitutes the canon of Scripture).

  This can also be called 'the Catholic Bible conundrum.' In that any attempt to prove the true Church from 'the Bible' already concedes that the Catholic Church had the authority to discern between Books and define the Canon for all Christians in the worldwide Church (which, again, historically speaking, is incontrovertible). And since a false Church has no authority to do this, but one did, and there is only one Church, then it is the Catholic Church which Jesus Christ founded, not any other.

On the other hand, an argument could be made that citing the fact that apostolic fathers (men who lived with directly, or lived with disciples of the Apostles taught things only Catholics still believe). And this isn't 'early people believed it so it's true,' it's that it's what the Apostles were teaching, or at the least, what could be matter-of-factly spoken of as Christianity in the first, second and third centuries, never to be questioned by later Christians (1500 years later is not a valid or realistic candidate, let's be honest here—that sounds suspiciously like a novelty, or heresy). It then only becomes a matter of whether the Eastern Orthodox or Catholics are the true Church in such a case, since only those really hold to the bishop, presbyter, deacon structure of the Church, as well as the Eucharist as a sacrifice, virgin Mary as new Eve, etc. In which case the Papacy becomes a deciding factor. And even then, the East always accepted and acted like it was true that the bishop of Rome was to be recoursed to in disputes and issues bishops who were closer to them couldn't. Arguably in Clement of Rome's case, even over a living Apostle (John).

In other words, the question is flawed because it asks the reader to overlook things which cannot be overlooked when determining the true faith—a doctrinal novelty (and on top of that, not just a new belief, but one which contradicts everything accepted as the true belief before it) can't just claim to be original, because you can read it into Scripture. It has to correspond to reality, history, and the way things are. What I mean by overlook is that even if you 'proved' to someone's satisfaction you were the true Church, once you take off the blindfold to history, you'll see there was no one who ever believed this.

Apart from any claim related to antiquity, does the modern Roman Catholic Church claim to be" The Body of Christ"?

The short answer is: Yes.

Pope Pius XII's encyclical Mystici Corporis Christi (Mystical Body of Christ) (June 29, 1943) should count as being on topic for this post? And, if so, keep reading.

Although Pope Pius XII states in his encyclical states that the true Church is which is the One, Holy, Catholic, Apostolic and Roman Church as being the Mystical body of Christ; he also states that the Universal Church comprises of the Latin and Eastern Rites.

13. If we would define and describe this true Church of Jesus Christ - which is the One, Holy, Catholic, Apostolic and Roman Church - we shall find nothing more noble, more sublime, or more divine than the expression "the Mystical Body of Christ" - an expression which springs from and is, as it were, the fair flowering of the repeated teaching of the Sacred Scriptures and the Holy Fathers.

(42) What we have thus far said of the Universal Church must be understood also of the individual Christian communities, whether Oriental or Latin, which go to makeup the one Catholic Church. For they, too, are ruled by Jesus Christ through the voice of their respective Bishops.

Of all the Eastern Rites Churches, the Maronite Catholic Church has never been separated from unity with the See of St. Peter. Thus indicating a small flaw in the title of this question as it is presented at this moment in time.

The Maronite Church is considered the only one of the Eastern Catholic Churches to have always remained in full communion with the Holy See, while most of the other churches unified from the 16th century onwards.

Before going on any further, I believe the word "Roman" should be used with caution. The reason being is that the first three centuries the liturgical language in Rome was Greek, not Latin. Some believe that it was St. Augustine who first brought in Latin in to the liturgy while in Africa. The Church has from her very foundation worshiped in several languages and still does. This is not an historical claim, but an historical fact and as such is permitted in this response.

The following is not an historical claim from antiquity, but an historical fact dating back to antiquity.

The first language of Christian liturgy was Aramaic, the common language of the first Christians, who were Palestinian Jews. While Hebrew was the language of scripture and formal worship, Christian worship occurred in the home where Aramaic was spoken. The words Abba and maranatha are Aramaic.

Christianity quickly spread from Palestine to the rest of the world, and the Eucharist came to be celebrated in many languages, including Syriac, Coptic, and Armenian. In most of the Mediterranean world, the common language was Greek, which became the language of liturgy in that region and remained so until the early third century.

Eucharist itself is a Greek word, meaning thanksgiving. The phrase Kyrie eleison and the words liturgy, baptism, evangelize, martyr, and catechumen, among other familiar church words, are also Greek in origin.

From around the third century B.C., what we call “classical” Latin was the language of the Roman aristocracy and the educated classes. Around the time Jesus was born, during the reign of Augustus Caesar, the language began to change. The Roman aristocracy was destroyed by war and political infighting; when they disappeared, their language went with them. Classical Latin was replaced by a less refined version of the language.

In the third and fourth centuries A.D. this form of Latin began to replace Greek as the common language of the Roman world and soon became the language of the liturgy.

Exactly how this change in the liturgy came about is uncertain. In the early church the liturgy was led extemporaneously by the bishop, according to a pattern. There were written examples of Eucharistic Prayers, but they were models, not prescribed prayers. The last such document in Greek was written around the year 215. By the sixth century, the Roman Canon (which is still in use, also called Eucharistic Prayer I) appears, completely in Latin and prescribed for use exactly as written. - When did we start celebrating Mass in Latin?

Now for responding to the question at hand: Apart from any claim related to antiquity, does the modern Roman Catholic Church claim to be "The Body of Christ"?

Yes.

Well it so happens that Pope Pius XII in his encyclical Mystici Corporis Christi (29 June 1943) affirms that the Catholic Church is in fact the Mystical Body of Christ. The pope is the head of the Catholic Church on earth whether of the Roman Rite or Eastern Rite Catholics. We are still one Church in Christ.

The Maronite Church is considered the only one of the Eastern Catholic Churches to have always remained in full communion with the Holy See, while most of the other churches unified from the 16th century onwards. However, the Melkite Catholic Church and the Italo-Albanian Greek Catholic Church also claim perpetual communion. Eastern Catholic Churches (Wikipedia)

Pope Pius XII boldly asserts that the Universal Church is made up of the Roman Rite and those of the Eastern Rites united to the See of St. Peter.

Mystici corporis Christi (29 June 1943) is a papal encyclical issued by Pope Pius XII during World War II, on the Church as the Mystical Body of Christ.2 It is one of the more important encyclicals of Pope Pius XII, because of its topic, the Church, and because its Church concept was fully included in Lumen gentium but also strongly debated during and after Vatican II. The Church is called body, because it is a living entity; it is called the body of Christ, because Christ is its Head and Founder; it is called mystical body, because it is neither a purely physical nor a purely spiritual unity, but supernatural.

The actual encyclical has much to say and here follows just a small sampling. One may peruse the entire encyclical at one's leisure (Mystici Corporis Christi):

The doctrine of the Mystical Body of Christ, which is the Church, was first taught us by the Redeemer Himself. Illustrating as it does the great and inestimable privilege of our intimate union with so exalted a Head, this doctrine by its sublime dignity invites all those who are drawn by the Holy Spirit to study it, and gives them, in the truths of which it proposes to the mind, a strong incentive to the performance of such good works as are conformable to its teaching.

(14) That the Church is a body is frequently asserted in the Sacred Scriptures. "Christ," says the Apostle, "is the Head of the Body of the Church." If the Church is a body, it must be an unbroken unity, according to those words of Paul: "Though many we are one body in Christ." But it is not enough that the Body of the Church should be an unbroken unity; it must also be something definite and perceptible to the senses as Our predecessor of happy memory, Leo XIII, in his Encyclical Satis Cognitum asserts: "the Church is visible because she is a body. Hence they err in a matter of divine truth, who imagine the Church to be invisible, intangible, a something merely "pneumatological" as they say, by which many Christian communities, though they differ from each other in their profession of faith, are untied by an invisible bond.

(15) But a body calls also for a multiplicity of members, which are linked together in such a way as to help one another. And as in the body when one member suffers, all the other members share its pain, and the healthy members come to the assistance of the ailing, so in the Church the individual members do not live for themselves alone, but also help their fellows, and all work in mutual collaboration for the common comfort and for the more perfect building up of the whole Body.

(22) Actually only those are to be included as members of the Church who have been baptized and profess the true faith, and who have not been so unfortunate as to separate themselves from the unity of the Body, or been excluded by legitimate authority for grave faults committed. "For in one spirit" says the Apostle, "were we all baptized into one Body, whether Jews or Gentiles, whether bond or free." As therefore in the true Christian community there is only one Body, one Spirit, one Lord, and one Baptism, so there can be only one faith. And therefore, if a man refuse to hear the Church, let him be considered - so the Lord commands - as a heathen and a publican. It follows that those who are divided in faith or government cannot be living in the unity of such a Body, nor can they be living the life of its one Divine Spirit.

(34) That this Mystical Body which is the Church should be called Christ's is proved in the second place from the fact that He must be universally acknowledged as its actual Head. "He," as St. Paul says, "is the Head of the Body, the Church." He is the Head from whom the whole body perfectly organized, "groweth and maketh increase unto the edifying of itself."

(42) What we have thus far said of the Universal Church must be understood also of the individual Christian communities, whether Oriental or Latin, which go to makeup the one Catholic Church. For they, too, are ruled by Jesus Christ through the voice of their respective Bishops. Consequently, Bishops must be considered as the more illustrious members of the Universal Church, for they are united by a very special bond to the divine Head of the whole Body and so are rightly called "principal parts of the members of the Lord;" moreover, as far as his own diocese is concerned, each one as a true Shepherd feeds the flock entrusted to him and rules it in the name of Christ. Yet in exercising this office they are not altogether independent, but are subordinate to the lawful authority of the Roman Pontiff, although enjoying the ordinary power of jurisdiction which they receive directly from the same Supreme Pontiff. Therefore, Bishops should be revered by the faithful as divinely appointed successors of the Apostles, and to them, even more than to the highest civil authorities should be applied the words: "Touch not my anointed one!" For Bishops have been anointed with the chrism of the Holy Spirit.

(66) And if at times there appears in the Church something that indicates the weakness of our human nature, it should not be attributed to her juridical constitution, but rather to that regrettable inclination to evil found in each individual, which its Divine Founder permits even at times in the most exalted members of His Mystical Body, for the purpose of testing the virtue of the Shepherds no less than of the flocks, and that all may increase the merit of their Christian faith. For, as We said above, Christ did not wish to exclude sinners from His Church; hence if some of her members are suffering from spiritual maladies, that is no reason why we should lessen our love for the Church, but rather a reason why we should increase our devotion to her members. Certainly the loving Mother is spotless in the Sacraments by which she gives birth to and nourishes her children; in the faith which she has always preserved inviolate; in her sacred laws imposed on all; in the evangelical counsels which she recommends; in those heavenly gifts and extraordinary grace through which with inexhaustible fecundity she generates hosts of martyrs, virgins and confessors. But it cannot be laid to her charge if some members fall, weak or wounded. In their name she prays to God daily: "Forgive us our trespasses;" and with the brave heart of a mother she applies herself at once to the work of nursing them back to spiritual health. When, therefore, we call the Body of Jesus Christ "mystical," the very meaning of the word conveys a solemn warning. It is a warning that echoes in these words of St. Leo: "Recognize, O Christian, your dignity, and being made a sharer of the divine nature go not back to your former worthlessness along the way of unseemly conduct. Keep in mind of what Head and of what Body you are a member."

Then there is the fact that the Church claims of Apostolic Succession; but because this question overtly refuses to allow such legitimate claims (in Antiquity) shows yet another flaw on the subject (wording in the title of this post) of the true Universal Body of Christ which is the Church.

The Pope is the Supreme Pontiff of the entire Catholic Church (Latin or Oriental) which is called the Mystical Body of Christ, yesterday and today.