~St. John Damascene
"And thus the immaculate (panagion)  body was laid in the tomb. Then it was assumed after three days to the heavenly mansions. The bosom of the earth was no fitting receptacle for the Lord's dwelling-place, the living source of cleansing water, the corn of heavenly bread, the sacred vine of divine wine, the evergreen and fruitful olive-branch of God's mercy. And just as the all holy body of God's Son, which was taken from her, rose from the dead on the third day, it followed that she should be snatched from the tomb, that the mother should be united to her Son; and as He had come down to her, so she should be raised up to Him, into the more perfect dwelling-place, heaven itself. It was meet that she, who had sheltered God the Word in her own womb, should inhabit the tabernacles of her Son."
~St. John Damascene, Homily II on the Assumption/Dormition
"To-day the living ladder, through whom the  Most High descended and was seen on earth, and conversed with men, was assumed into heaven by death. To-day the heavenly table, she, who contained the bread of life, the fire of the Godhead, without knowing man, was assumed from earth to heaven, and the gates of heaven opened wide to receive the gate of God from the East. To-day the living city of God is transferred from the earthly to the heavenly Jerusalem, and she, who, conceived her first-born and only Son, the first-born of all creation, the only begotten of the Father, rests in the Church of the first-born: the true and living Ark of the Lord is taken to the peace of her Son. The gates of heaven are opened to receive the receptacle of God, who, bringing forth the tree of life, destroyed Eve's disobedience and Adam's penalty of death. And Christ, the cause of all life, receives the chosen mirror, the mountain from which the stone without hands filled the whole earth. She, who brought about the Word's divine Incarnation, rests in her glorious tomb as in a bridal-chamber, whence she goes to the heavenly bridals, to share in the kingdom of her Son and God, leaving her tomb as a place of rest  for those on earth."
~St. John Damascene, Homily III on the Assumption/Dormition
 And all the days of Henoch were three hundred and sixty-five years.  And he walked with God, and was seen no more: because God took him.
4 Kings 2:11:
 And as they went on, walking and talking together, behold a fiery chariot, and fiery horses parted them both asunder: and Elias went up by a whirlwind into heaven.
"Thou wert not taken into heaven as Elias was, nor didst thou penetrate to the third heaven with Paul, but thou didst reach the royal throne itself of thy Son, seeing it with thy own eyes, standing by it in joy and unspeakable familiarity."
~St. John Damascene, Homily I on the Assumption/Dormition
Praised be Jesus Christ!
Now and forever. Amen.
So, we come to the single mystery for which there is no historical account in Scripture. This mystery is, however, attested to within Christian Tradition, and has been defined as Dogma in the Catholic Church (Pope Pius XII, Munificentissimus Deus). This mystery is known as the Dormition (sleep) in the Eastern Churches, and has also been known as the Pausatio (pausing, or end), Mors (death), and Depositio (laying down) of Mary.
The tradition is that Mary reached the end of her life (the timing is uncertain--between three and fifteen years after the Ascension), and was put in a tomb by the Apostles, but when her tomb was opened later, it was found to be empty. Their conclusion, coming from both their Jewish tradition and from the revelation of Jesus Resurrection, was that her body had been raised and taken to Heaven.
I admit that I'm not going to delve too deeply into this mystery, but I do want to touch upon a couple of points. I want to explore the meaning of Mary's death, as well as to make the point that this idea of her being taken bodily to heaven is not a novelty within the Jewish tradition. However, if you want a more thorough reflection on this mystery, I welcome you to read the homilies by St. John Damascene, who lived in the 7th-8th century. They can be found here, here, and here.
Throughout my childhood and youth and into my young adulthood, I had been taught the Assumption of the Blessed Virgin, and I had believed it. However, during all of that time, it had never been made known to me that it is part of Christian Tradition that Mary had died before being assumed into heaven. So, it came as something of a shock to me to find out this is something the Catholic Church has always believed and taught. I had even heard about the Eastern belief in the Dormition, but still, it wasn't clear to me that she had died.
When I learned about this, I was of course immediately curious. I had always understood Mary's Assumption as having occurred because of Mary's sinlessness, and that she was not subject to corruption and death. So, finding out that she did, indeed, die forced me to re-examine that belief.
So, I reflected on it. I had discussions about it with other believers. The conclusion I arrived at, and St. John Damascene affirms in his homilies, is that Mary was indeed free from corruption and death, but that she chose to accept the death of her body in conformity with the will of God, who declared the consequence for Adam and Eve's sin to be death. I concluded that, just as Jesus had accepted death, had accepted this consequence of sin, in order to restore right order to our humanity, so too did Mary accept death in unity with her Son.
St. John Damascene offers many other reasons, reasons from "fittingness", that Mary died. He demonstrates that Mary is the fulfillment of many types from the old testament, Jacob's Ladder, the Ark of the Covenant, the Living City, and others, and that it is fitting that she enter into God's abode as the fulfillment of these types.
It made me wonder about God's original plan for humanity. We know that God bestowed the preternatural grace of immortality upon Adam and Eve in their original innocence, but I wonder if, understanding the nature of the material world as temporary, that God intended them originally to submit themselves to the death of the body in respect of its nature. Ah, speculations....
Within the Jewish Tradition
The second thing I wanted to touch upon was the idea that Mary being taken up to heaven body and soul would not have been thought of as novel by the early Jewish Christians. Within Jewish Scriptures, there are two other figures who were also taken up into heaven bodily: Enoch and Elijah. These were known for their righteousness before God, and Elijah is arguably the most important prophet in Jewish history. It is not, therefore, out of place to believe that the woman who surpassed all Old Testament saints and prophets would also have been taken up into heaven, body and soul.
I think this makes all the more sense when we understand it in light of Jesus' own resurrection, and His promise of resurrection at the end of time. Mary's resurrection and assumption into heaven represents the first eschatological fruit of Jesus' promise, of His saving work on the Cross, and His victory over death. His resurrection is proof of His victory over death, and her resurrection is proof that His victory belongs to all of us, who live in His love.
In Him, we will rise to new life, and live in His joy for ever. Praise be to Him, the Ancient of Days! Blessed be His mother, who lives with Him even now!
God bless you, and gratias vobis ago!