The Assumption of the Blessed Virgin Mary into heaven is a dogmatic tradition of Apostolic origin.
Among the feasts of the Saints this is the solemnity of solemnities. "Let the mind of man," says St.Peter Damian, "be occupied in declaring her magnificence; let his speech reflect her majesty. May the sovereign of the world deign to accept the good will of our lips, to aid our insufficiency, to illumine with her own light the sublimity of this day"
In his instructions to the newly-converted Bulgarians, Pope St. Nicholas I, who occupied the Apostolic See from 858 to 867, had already united these four solemnities (Christmas, Easter, Pentecost and the Assumption) when recommending the fasts of Lent, of the Ember days, and of the Vigils of these feasts: "Fasts," he says, "which the holy Roman Church has "long since received and observed."
St. Jerome eloquently declared the grandeur of this feast : "Incomparable as is she who thereon ascended glorious and happy to the sanctuary of heaven: a solemnity, the admiration of the heavenly hosts, the happiness of the citizens of our true country, who, not content with giving it one day as we do, celebrate it unceasingly in the eternal continuity of their veneration, of their love, and of their triumphant joy."
Certain ancient calendars give this feast the title of Sleep or Repose, dormitio or pausatio of the Blessed Virgin. The Greeks, from whom we have the expression, have always included in the solemnity the glorious triumph that followed her death. The same is to be said of the Syrians,
Chaldeans, Copts, and Armenians.
Thus the Supreme Pontiff, Pope Pius XII, pastor of all Christians and head of the Universal Church solemnly proclaimed in his declaration, Munificentissimus Deus, 1 November 1950: "By the authority of our Lord Jesus Christ, of the Blessed Apostles Peter and Paul, and by our own authority, we pronounce, declare, and define it to be a divinely revealed dogma: that the Immaculate Mother of God, the ever Virgin Mary, having completed the course of her earthly life, was assumed body and soul into heavenly glory."
Sancta dei genitrix ora pro nobis!