This is an excerpt from the Apostolic Constitution of Pope Pius XII Munificentissimus Deus (AAS 42 , 760-762, 767-769) which defined the Assumption of Mary, long taught by the ordinary magisterium of the Church, as a dogma of faith.
In their sermons and speeches on the feast day of the Assumption of the Mother of God, the holy fathers and the great doctors of the church were speaking of something that the faithful already knew and accepted: all they did was to bring it out into the open, to explain its meaning and substance in other terms. Above all, they made it most clear that this feast commemorated not merely the fact that the blessed Virgin Mary did not experience bodily decay, but also her triumph over death and her heavenly glory, following the example of her only Son, Jesus Christ.
Thus St. John Damascene, who is the greatest exponent of this tradition, compares the bodily Assumption of the revered Mother of God with her other gifts and privileges: It was right that she who had kept her virginity unimpaired through the process of giving birth should have kept her body without decay through death. It was right that she who had given her Creator, as a child, a place at her breast should be given a place in the dwelling-place of her God. It was right that the bride espoused by the Father should dwell in the heavenly bridal chamber. It was right that she who had gazed on her Son on the cross, her heart pierced at that moment by the sword of sorrow that she had escaped at his birth, should now gaze on him seated with his Father. It was right that the Mother of God should possess what belongs to her on and to be honored by every creature as the God’s Mother and handmaid.
St Germanus of Constantinople considered that the preservation from decay of the body of the Mother of God, the Virgin Mary, and its elevation to heaven as being not only appropriate to her Motherhood but also to the peculiar sanctity of its virgin state: It is written, that you appear in beauty, and your virginal body is altogether holy, altogether chaste, altogether the dwelling-place of God; from which it follows that it is not in its nature to decay into dust, but that it is transformed, being human, into a glorious and incorruptible life, the same body, living and glorious, unharmed, sharing in perfect life.
Another very ancient author asserts: Being the most glorious Mother of Christ our savior and our God, the giver of life and immortality, she is given life by him and shares bodily incorruptibility for all eternity with him who raised her from the grave and drew her up to him in a way that only he can understand.
All that the holy fathers say refers ultimately to Scripture as a foundation, which gives us the vivid image of the great Mother of God as being closely attached to her divine Son and always sharing his lot.
It is important to remember that from the second century onwards the holy fathers have been talking of the Virgin Mary as the new Eve for the new Adam: not equal to him, of course, but closely joined with him in the battle against the enemy, which ended in the triumph over sin and death that had been promised even in Paradise. The glorious resurrection of Christ is essential to this victory and its final prize, but the blessed Virgin’s share in that fight must also have ended in the glorification of her body. For as the Apostle says: When this mortal nature has put on immortality, then the scripture will be fulfilled that says “Death is swallowed up in victory”.
So then, the great Mother of God, so mysteriously united to Jesus Christ from all eternity by the same decree of predestination, immaculately conceived, an intact virgin throughout her divine motherhood, a noble associate of our Redeemer as he defeated sin and its consequences, received, as it were, the final crowning privilege of being preserved from the corruption of the grave and, following her Son in his victory over death, was brought, body and soul, to the highest glory of heaven, to shine as Queen at the right hand of that same Son, the immortal King of Ages.
This excerpt of Munificentissimus Deus (AAS 42 , 760-762, 767-769) by which Pope Pius XII defined the Assumption of Mary as a dogma of faith, is used in the Roman Office of readings for the Solemnity of the Assumption on August 15.