Pius XII states in the constitution "Munificentissimus Deus," which defined belief in the Assumption as a matter of faith:

"All the arguments and considerations of the Fathers and theologians rest on Sacred Scripture for their ultimate foundation. The Scriptures present the beloved Mother of God as most intimately united with her divine Son as ever sharing in his lot. Hence, it seems all but impossible to see her who conceived Christ. . .as separated from him, if not in soul, yet in body, after her life on earth was over. . .Seeing that by preserving her from the corruption of the tomb he could give her such great honor, we must believe that he actually did so."

St. John Damascene (d. 749) called the Doctor of the Assumption, writes, "On this day the sacred and life-filled ark of the living God, she who conceived her Creator in her womb, rests in the Temple of the Lord that is not made with hands. David, her ancestor, leaps, and with him the angels lead the dance."
Documentation testifies that the feast was celebrated first in the Eastern Church in the second half of the sixth century. Pope Sergius I (687-701) ordered its observance in Rome. At first it was kept as a memorial of Mary's death, her falling asleep (dormition), and it gradually came to be a commemoration of her Assumption as such.

Blessed Feast of Assumption ( August 15 )

This is the most ancient and solemn of the Blessed Virgin Mary's feasts. After a most blessed death Our Lady was triumphantly assumed into Heaven with her immaculate soul and pure body, and was crowned Queen of Heaven by Her own Divine Son.

Let us unite our joy and gratitude with that of the angels and saints in Heaven, as well as that of the Church upon earth, for it is our Heavenly Mother's Assumption Day.

How well did she deserve this immortal crown!

She crushed the serpent's head; she offered herself and her beloved Son unto death for the Redemption of mankind.

She triumphed over the world and the evil.

Let us pray that the Immaculate Virgin Mary may reign as Queen in our hearts, and in the hearts of all mankind. Let us pray to her for the grace of final perseverance in good and a happy death , also let us faithfully pray :
Almighty and everlasting God, Who hast taken up the Immaculate Virgin Mother of Thy Son, with Body and Soul into the heavenly Glory, grant, we beseech Thee, that we may, always intent on higher things, deserve to be partakers of Her Glory.
Through the same Our Lord Jesus Christ, Thy Son, Who liveth and reigneth with Thee, in the Unity of the Holy Ghost, One God, forever, unto ages of ages. Amen.

Hymn

Thou Guide of virgin hosts, Fair Mother of the Lord,
Who gavest back what Adam lost, earth's Hope and Heaven's Reward.

Thou Lily'mid the thorns, thou snowy-plumed Dove,
Thou budding Rod that God adorns with healing fruit of love.

Thou unassailed Tower, thou Star that breakest night,
From evil shield us by Thy power, and lead us by Thy light.

The shades of sin dispel, the hidden snares remove,
And midst the ocean's surging swell, a saving pathway prove.

Be praise and honor meet to Jesus, Virgin-born,
To Father and to Paraclete, throughout the endless morn. Amen.

V. Pray for us, O Queen of the Heavens,
R. That we may be made worthy of the promise of Christ.

May the offering of our devotion ascend to Thee, O Lord, and through the intercession of the most blessed Virgin Mary, who was taken up into Heaven, may our hearts be inflamed with the fire of Love, and continually long for Thee.

Through Our Lord Jesus Christ, Thy Son, Who liveth and reigneth with Thee, in the Unity of the Holy Ghost, One God, forever, unto ages of ages. Amen.