In speaking, thus, our Universal Shepherd was declaring the Assumption of Mary to be an article or dogma of Catholic faith. The Pope's declaration did not answer the question of whether Mary actually died or not prior to her Assumption.
When Pius XII declared the Assumption of Mary to be a dogma or doctrine of the church, he was not proposing for belief a tenet of faith that Catholics had never heard of before. Belief in Mary's Assumption into heaven goes back to at least the sixth century.
If Mary was without sin there was no reason for the resurrection of her body to be delayed. As with the doctrine of the Immaculate Conception, our church believes that it was "fitting" that the body which tabernacled or housed the Savior of the World should not suffer decay. It is "fitting" that she who gave birth to Jesus should be with him bodily in heaven where she adores him in the glory of his risen and glorified body. In reflecting about this doctrine of our church, it may be helpful to keep in mind that it is not without precedence. The Hebrew Scriptures tell us that both Enoch (Genesis 5:24 & Sirach 49:14) and Elijah (2 Kings 2:1-12) were taken bodily into heaven.
In the doctrine of the Assumption, The church tells us that God wishes to save not just our souls but also our bodies. Mary in her heavenly state stands as a symbol of the first fully redeemed person-soul and body. Mary's assumption is a reminder of what is in store for all of us. The church celebrates this feast of Mary on August 15.