The Assumption of Mary was infallibly defined by Pope Pius XII (1876-1958 AD) as a dogma in his Encyclical Munificentissimus Deus:
Pope Pius XII - Munificentissimus Deus (1950 AD)
44 By the authority of our Lord Jesus Christ, of the Blessed Apostles Peter and Paul, and by our own authority, we pronounce, declare, and define it to be a divinely revealed dogma: that the Immaculate Mother of God, the ever Virgin Mary, having completed the course of her earthly life, was assumed body and soul into heavenly glory.
45 Hence if anyone, which God forbid, should dare willfully to deny or to call into doubt that which we have defined, let him know that he has fallen away completely from the divine and Catholic Faith.
47 It is forbidden to any man to change this, our declaration, pronouncement, and definition or, by rash attempt, to oppose and counter it. If any man should presume to make such an attempt, let him know that he will incur the wrath of Almighty God and of the Blessed Apostles Peter and Paul.
Above is one of the few Papal declarations that is universally recognized to be Ex Cathedra - the Pope employing the power, as defined by Vatican 1 (1870 AD), to infallibly define dogma, which must be believed by all the faithful on pain of Anathema. It teaches that it is required to believe that Mary was bodily assumed to Heaven, either before or after her death.
Before getting into the Biblical and historical arguments surrounding this doctrine, are we allowed to ask what exactly changed in 1950 AD? Did God wait over 1,900 years to let His Church know that this was a divinely-revealed dogma which must be believed by everyone? Why? Why was a person allowed to disbelieve it in 1949, but not in 1950? Was new evidence forthcoming? Was new insight into the Scripture unveiled? The text of the pronouncement mentions thousands of petitions from laity and clergy for the definition. Is that what made it binding on all of mankind? Petitions? Will we go to Hell in 1950 for something that we would not have gone to Hell in 1949 for, because of a petition drive?
Now that the doctrine has been defined, and all those who disbelieve it are declared to have "fallen away completely from the divine and Catholic Faith", and all those who may attempt to oppose it are declared to have invoked "the wrath of Almighty God", let's investigate the Biblical and historical circumstances of this doctrine.
There is no Biblical evidence whatsoever for Mary's Assumption. Having dealt a lot with Islam, I recognize the tactics employed by those who need to find something in the Bible that isn't there. This is what we are dealing with - typology only - which can be used to tear the Bible into smithereens. Typology can support clear statements, but not serve as the foundation for something never stated anywhere in the text.
The last we hear of Mary, she is in a room with the disciples after Jesus's ascension, before Pentecost (Acts 1:13-14). That's it. No other details of her life are given in any of the epistles, some of which likely postdate her death. John's epistles are dated toward the very end of the 1st century, which would certainly postdate her death, unless she lived to be over 100 years old. Yet, not a word on the Assumption.
The Assumption would be the most important event to happen since Pentecost. God deciding to raise a person bodily to Heaven before all the rest of mankind (1 Corinthians 15:20-23) would be a miracle on par, or far exceeding, anything that we see in the New Testament after Christ's ascension. Yet, there is not a prophecy, nor a reference - much less an actual account - of the event. Why? If Christians have to believe this, or go to Hell, why didn't God put it in the Bible?
The arguments by Catholics for the Assumption depend entirely on a specific interpretation thrust upon various types, primarily the Ark of the Covenant. The Bible verse quoted by the Pope in the definition is:
Psalm 132:7-9
7 We will go into his tabernacles: we will worship at his footstool.
8 Arise, O LORD, into thy rest; thou, and the ark of thy strength.
9 Let thy priests be clothed with righteousness; and let thy saints shout for joy.
We are to believe, based on the above, that Mary was taken bodily to Heaven. It has been bound on the soul of every Christian, just as much as the death and resurrection of Jesus, because it is De Fide. Yet, it has no Biblical support whatsoever, and the verses offered as proof texts are an insult to anyone who even pretends to be concerned with the truth of God's Word.
Just as Mary's Assumption is absent from the Bible, it is also entirely absent from the earliest Christian writers - many of whom discuss Mary in detail, exalt her, and extol her perpetual virginity - which was a very early Marian doctrine. Yet, nothing of the miracle of the Assumption.
This cannot just be dismissed as an invalid argument from silence. An invalid argument from silence would be if Mary never came up in any of these writings. But, she did. Discussion of her, her holiness, her life, and her death is found in abundance, and never once is her bodily assumption mentioned.
For instance, Augustine (354-430 AD) mentions her death in passing, without feeling the need to qualify it in terms of the Assumption:
Augustine (354-430 AD) - Tractate 8 (John 2:1-4)
9 There was there near the cross the mother of Jesus; and Jesus says to His mother, Woman, behold your son! And to the disciple, Behold your mother! He commends His mother to the care of the disciple; commends His mother, as about to die before her, and to rise again before her death. The man commends her a human being to man's care. This humanity had Mary given birth to. That hour had now come, the hour of which He had then said, Mine hour is not yet come.
Then, to give an example of one of the many dozens of passages which speak of Mary, and exalt her, which can be found in the early Christian writers, we can read:
Gregory Thaumaturgus (213-270 AD) - Second Homily on the Annunciation to the Holy Virgin Mary
It is our duty to present to God, like sacrifices, all the festivals and hymnal celebrations; and first of all, the annunciation to the holy mother of God, to wit, the salutation made to her by the angel, "Hail, thou that art highly favoured!" For first of all wisdom and saving doctrine in the New Testament was this salutation, "Hail, thou that art highly favoured!" conveyed to us from the Father of lights. And this address, "highly favoured," embraced the whole nature of men. "Hail, thou that art highly favoured" in the holy conception and in the glorious pregnancy, "I bring you good tidings of great joy, which shall be to all people." And again the Lord, who came for the purpose of accomplishing a saving passion, said, "I will see you, and ye shall rejoice; and your joy no man taketh from you."
And after His resurrection again, by the hand of the holy women, He gave us first of all the salutation "Hail!" And again, the apostle made the announcement in similar terms, saying, "Rejoice evermore: pray without ceasing: in everything give thanks." See, then, dearly beloved, how the Lord has conferred upon us everywhere, and indivisibly, the joy that is beyond conception, and perennial. For since the holy Virgin, in the life of the flesh, was in possession of the incorruptible citizenship, and walked as such in all manner of virtues, and lived a life more excellent than man's common standard; therefore the Word that cometh from God the Father thought it meet to assume the flesh, and endue the perfect man from her, in order that in the same flesh in which sin entered into the world, and death by sin, sin might be condemned in the flesh, and that the tempter of sin might be overcome in the burying of the holy body, and that therewith also the beginning of the resurrection might be exhibited, and life eternal instituted in the world, and fellowship established for men with God the Father.
Again, above is just one example of many early passages in which Mary is extolled. Yet, in none of these passages is there ever a mention of what would be the most important event of her life, outside of the birth of Christ.
Apart from passages discussing Mary, there are also passages discussing those who were assumed to Heaven by God. Notice how well a mention of Mary's Assumption would fit here:
Irenaeus (130-202 AD) - Against Heresies, Book 5, Chapter 5
1 [In order to learn] that bodies did continue in existence for a lengthened period, as long as it was God's good pleasure that they should flourish, let [these heretics] read the Scriptures, and they will find that our predecessors advanced beyond seven hundred, eight hundred, and nine hundred years of age; and that their bodies kept pace with the protracted length of their days, and participated in life as long as God willed that they should live. But why do I refer to these men? For Enoch, when he pleased God, was translated in the same body in which he did please Him, thus pointing out by anticipation the translation of the just. Elijah, too, was caught up [when he was yet] in the substance of the [natural] form; thus exhibiting in prophecy the assumption of those who are spiritual, and that nothing stood in the way of their body being translated and caught up. For by means of the very same hands through which they were moulded at the beginning, did they receive this translation and assumption.
Mary's Assumption, had Irenaeus been aware of such a thing, would have been a fantastic third example of assumption for him - and a New Testament one, at that. Yet, nothing at all.
Another example of an early writer discussing God's assumption of people:
Tertullian (160-220 AD) - On the Resurrection of the Flesh, Chapter 58
Enoch and Elias, who even now, without experiencing a resurrection (because they have not even encountered death), are learning to the full what it is for the flesh to be exempted from all humiliation, and all loss, and all injury, and all disgrace - translated as they have been from this world, and from this very cause already candidates for everlasting life; - to what faith do these notable facts bear witness, if not to that which ought to inspire in us the belief that they are proofs and documents of our own future integrity and perfect resurrection? For, to borrow the apostle's phrase, these were "figures of ourselves;" and they are written that we may believe both that the Lord is more powerful than all natural laws about the body, and that He shows Himself the preserver of the flesh the more emphatically, in that He has preserved for it its very clothes and shoes.
Here, Tertullian presents Enoch and Elijah as "figures of ourselves", namely, "our own future integrity, and perfect resurrection". Mary, had she been assumed to Heaven, would have an extremely obvious third example, but isn't mentioned, because the doctrine of her Assumption had not developed yet. There are many similar examples.
How can it be that we have volumes of early Christian writings - 10 volumes of the Ante-Nicene writers alone - all of which are devoid of this significant event, if it were universally known? Mary is mentioned over 300 times in the Ante-Nicene writers, yet none of them give so much as a hint about the Assumption, which would have been the most significant miracle since Pentecost. Why?
Finally, the most significant early passage on this matter is found in the works of Epiphanius of Salamis (310-403 AD). He wrote a compendium of refutations to 80 heresies that were present at his time, and in this work, he writes:
Epiphanius (310-403 AD) - The Panarion, Antidicomarians
23.8 And there have been many such things to mislead the deluded, though the saints are not responsible for anyone's stumbling; the human mind finds no rest, but is perverted to evils. The holy virgin may have died and been buried - her falling asleep was with honor, her death in purity, her crown in virginity. Or she may have been put to death - as the scripture says, "And a sword shall pierce through her soul" - her fame is among the martyrs and her holy body, by which light rose on the world, [rests] amid blessings. Or she may have remained alive, for God is not incapable of doing whatever he wills. No one knows her end.
But we must not honor the saints to excess; we must honor their Master. It is time for the error of those who have gone astray to cease. Mary is not God and does not have her body from heaven but by human conception, though, like Isaac, she was provided by promise. And no one should make offerings in her name, for he is destroying his own soul. But neither, in turn, should he be insolent and offer insult to the holy Virgin. Heaven forbid, she had no sexual relations after or before the Savior's conception.
Here, Epiphanius ponders on how Mary died, says that he does not know, and that "No one knows her end". This completely refutes the notion that there was a universal apostolic tradition regarding the life and Assumption of Mary. He demonstrates that he knows only as much as Scripture would tell us about Mary - which is to say, nothing at all about her later life.
This passage from Epiphanius is otherwise significant for a few reasons:
Because the Assumption of Mary is missing from early Christian writers, appeals are often made to Dormition narratives, which are apocryphal accounts of the end of Mary's life. The earliest and most significant of these is generally thought to be The Book of Mary's Repose, which Shoemaker dates to "the early fifth century at the absolute latest and most likely even earlier" (Mary in Early Christian Faith and Devotion, Chapter 3, pg. 102).
The Book of Mary's Repose would be considered heterodox by Catholics, as in it, among other things, Mary states "And because of this I fear: because I did not believe in my God for even one day. Behold, I will tell you about my sin", and has Jesus saying to her, "Mary, my mother, every sin is imputed to you, because you have tasted the bitter as the sweet". It is a lengthy text which contains pages of fraudulent dialogue from the Lord, the Apostles, and Mary, and one has to ponder the wickedness of any individual who would presume to put so many words in the mouths of others, especially the Lord.
However, it is worth noting that Shoemaker says that the corpus of Dormition narratives is comprised of "some forty different texts scattered across nine different ancient and medieval languages" (Mary in Early Christian Faith and Devotion, Chapter 3, pg. 100). In this, readers of early Christian apocrypha will recognize parallels with the many so-called Infancy Gospels of Jesus, in which a period of time of which authentic revelation is silent - the early years of the Lord's life - is filled in with wonderful, fraudulent details by those who are not content with God's silence on the period in question. This is the purpose of these Dormition narratives, though instead of forging details about the early life of Jesus, they forge details about the end of Mary's life.
In summary, the above demonstrates the lack of early history for the doctrine of the Assumption. It is nowhere in the Bible, and nowhere in early Christian writings. Rather, it crept in via fraudulent narrative traditions about the end of Mary's life, which were written centuries after the life of Mary, and are no more trustworthy than the similarly-purposed Infancy Gospels of the Lord.
The Roman Catholic Church, over 1,900 years after Jesus Christ, bound a doctrine to the minds of all believers, on pain of Hellfire, that is utterly unbiblical, and ahistorical. It is a late accretion, which arose out of heretical works, and has nothing to do with the Biblical Mary. Mandating that all people believe it is one of the most violent, egregious attacks on Galatians 1:6-9 in the history of the Church.
The definition of the Assumption was also the first Ex Cathedra statement made after Vatican 1 established Papal Infallibility. Yet, it is Biblically, and historically, indefensible. The entire Roman Catholic doctrine of Papal Infallibility from which this issue stems is itself offensive to God and reason, as Catholics ascribe infallibility to a single person in matters of faith and morals, yet that person - and all those who have held his position for the last 1,500 years - has failed to provide the Church with so much as a simple infallible Bible commentary. Instead, he speaks Ex Cathedra once every few hundred years, to define such indefensible doctrines as the Assumption, and condemn all other Christians to Hell if they reject it.