The Church has received the tradition of the Dormition (death) and Assumption into heaven of the Mother of God from the ancient Fathers of the Church.
When the Savior was pleased to take His Mother to Himself in heaven, He sent the Archangel Gabriel to her once again. He revealed to her that she would be taken from this earthly life into paradise. At hearing this, she gave thanks and hurried to the Mount of Olives, where she gave herself over to prayer. Meanwhile, the Apostles (who had traveled throughout the world to preach) were taken up by clouds and were gathered to the Virgin's house. She consoled them, blessed them, and prayed that peace would come upon the world.
When the time for her departure arrived, she quietly rested upon her bed and gave up her spirit into the hands of her Son. The Apostles, accompanied by the chanting of angels, reverently carried her undefiled body to the tomb and buried it. Three days later, as they were eating the eucharistic meal together, the Theotokos appeared to them in her glorified body. They went to her tomb, and found it empty except for her belt and a heavenly fragrance.
In this feast, we see the assurance of the Universal Resurrection. By divine dispensation, the Mother of God receives her glorified body even before the Second Coming of her Son. She is an icon of the hope we have for ourselves and all faithful believers.