We find homilies on the Assumption going back to the sixth century. In following centuries the Eastern Churches held steadily to the doctrine, but some authors in the West were hesitant. However, by the thirteenth century there was universal agreement. The feast was celebrated under various names (Commemoration, Dormition, Passing, Assumption) from at least the fifth or sixth century.
Scripture does not give an account of Mary’s Assumption into heaven. Nevertheless, Revelation 12 speaks of a woman who is caught up in the battle between good and evil. Many see this woman as God’s people. Since Mary best embodies the people of both Old and New Testament, her Assumption can be seen as an exemplification of the woman’s victory.
Furthermore, in 1 Corinthians 15:20 Paul speaks of Christ’s resurrection as the firstfruits of those who have fallen asleep.
Since Mary is closely associated with all the mysteries of Jesus’ life, it is not surprising that the Holy Spirit has led the Church to belief in Mary’s share in his glorification. So close was she to Jesus on earth, she must be with him body and soul in heaven.