Among the feasts of the Blessed Virgin that of the dormitio sanctae Mariae, or of her bodily assumption into heaven, was from very early times the most solemn and the most widely observed. In the time of Pope Sergius I a solemn procession proceeded to St. Mary Major, where Mass was celebrated. It was customary to carry images of the Savior and of His Blessed Mother in this procession; outside of Rome a similar ceremony was observed.
It should, however, be borne in mind
that though the divine maternity of the Blessed Virgin Mary may be regarded as the immediate reason of her Assumption into heaven, yet the first and formal reason of this privilege is to be sought in her Immaculate Conception. It is true, indeed, that the dignity of the Mother of the Incarnate Word was the primary reason for which God preserved the Immaculate Conception of Mary from all stain of original sin- and in this sense the Gregorian Sacramentary rightly attributes the reason of the bodily resurrection of the Blessed Virgin to her prerogative as Mother of the Word- but in order to express this truth with perfect accuracy, it is necessary to say that the formal reason for the preservation of her body from corruption was precisely her immunity from all stain of original sin.
The consecrated formulas of the Roman Liturgy have not any difficulty in expressing and in reconciling the fact of the death of the Blessed Virgin with her bodily resurrection, due to her exalted dignity.
The end of that transitory state in which the pilgrim soul finds itself on earth is called by us death, but it does not necessarily imply any idea of pain or abasement in the case of the Immaculate Mother of God. The state of separation of soul and body with all its consequences, such as bodily corruption, long and violent separation of form from matter, etc. had not power over the Mother of God.
The authority of the Roman Liturgy concerning the possibility of dogmatic definition of the Assumption of the Blessed Virgin is paramount, for it reflects the teaching and authority of the supreme Pontiff. Now that Catholic devotion anticipates the day when the infallible Teacher of Truth will place this last gem in the diadem which adorns Our Lady in heaven, theologians will be able to draw largely on that fount of Catholic tradition which is contained in the Liturgy, especially that of Rome.
(Source: The New Roman Missal, Rev. F. X. Lasance)