August 15 is the day that Catholics have long celebrated what is called the Dormition (falling asleep) or Assumption of the Virgin Mary. The Feast of the Assumption celebrates both the happy departure of Mary from this life by her natural death, and her assumption bodily into heaven.
Now at the end of the summer season, the Church celebrates the most glorious "harvest festival" in the Communion of Saints -- Mary, the supremely blessed one among women, Mary, the most precious fruit which has ripened in the fields of God's kingdom, is today taken into heaven.
There is an important difference, of course, between the ascension of Jesus into Heaven after His Resurrection, and the assumption of Mary. To ascend is to rise up under one's own power; while to be assumed means something that is done to one. Jesus, being the Second Person of the Trinity, had no need of assistance; whereas Mary did not have this power. (A pastor once demonstrated this difference in an unusual way. He asked two children to come to the front of the church. He told one child to walk from one side of the sanctuary to the other; and the other child he carried across.)
According to one tradition, Mary was warned of her approaching end by Saint Michael the Archangel, who conducts souls to Heaven, and was surrounded on her death-bed by the apostles, who were miraculously transported to her bedside from their various mission-fields. It was said that Jesus appeared, bore away her soul, and returned three days after her burial, when angels carried her body to Paradise where it was reunited with her soul under the Tree of Life.
For the Feast of the Assumption Hymn: The Ark which God has Sanctified The ark which God has sanctified, Which He has filled with grace, Within the temple of the Lord Has found a resting-place.
More glorious than the seraphim, This ark of love divine, Corruption could not blemish her Whom death could not confine.
God-bearing Mother, Virgin chaste, Who shines in heaven's sight; She wears a royal crown of stars Who is the door of Light.
To Father, Son and Spirit blest may we give endless praise With Mary, who is Queen of heaven, Through everlasting days. - from Stanbrook Abbey Hymnal