As St. Thomas observes, sin consists in a two-fold element, namely, the turning away from God and the turning toward inordinately creatures. The formal element of original sin is the privation of original justice, which resulted in the will turning away from God. The material element is concupiscence, whereby the will is turned toward creatures. St. Thomas explains:
“Everything takes its species from its form: and it has been stated that the species of original sin is taken from its cause. Consequently the formal element of original sin must be considered in respect of the cause of original sin. But contraries have contrary causes. Therefore the cause of original sin must be considered with respect to the cause of original justice, which is opposed to it. Now the whole order of original justice consists in man's will being subject to God: which subjection, first and chiefly, was in the will, whose function it is to move all the other parts to the end, as stated above (Question 9, Article 1), so that the will being turned away from God, all the other powers of the soul become inordinate. Accordingly the privation of original justice, whereby the will was made subject to God, is the formal element in original sin; while every other disorder of the soul's powers, is a kind of material element in respect of original sin. Now the inordinateness of the other powers of the soul consists chiefly in their turning inordinately to mutable good; which inordinateness may be called by the general name of concupiscence. Hence original sin is concupiscence, materially, but privation of original justice, formally.”
At Baptism, the formal element of original sin is partially removed through the infusion of sanctifying grace and charity into the soul; but, due to the loss of the preternatural gift of bodily integrity (which kept man’s lower nature perfectly subject to his higher nature), the material element remains, and must be combated by the reception of the sacraments, self denial, and the practice of virtue. By a singular privilege, the Virgin Mary was preserved from all stain of original sin – not only the formal element, but the material element as well. As such, the Blessed Virgin Mary was free from concupiscence, which impedes the pure and perfect love of God, for she was truly “full of grace” (Luke 1:28). “It was not fitting”, wrote St. Bernadine of Sienna, “that He, the Son of God, would be born of a Virgin, and take her flesh, were she in the slightest decree stained with original sin.”
This privilege was granted to the Blessed Mother through the merits of her Son, our Lord Jesus Christ, who was indeed her Savior (Luke 1:47); but unlike others who are saved by being cleansed from sin through the merits of Christ, the Blessed Mother was saved through His merits by being preserved from sin. In fulfillment of the prophecy of Gen. 3:15 – “I will put enmity between thee and the woman” – the Blessed Mother was exempted from the universal law of sin that passed onto all men due to the transgression of Adam, the father of the human race. It was fitting that she, who was destined to crush the head of serpent – “she shall crush thy head” (Gen. 3:15) – should be free from all stain of sin, so that he, whose head she will crush, would never have any place in her. Referring to the Blessed Virgin Mary, St. John Damascene said “the serpent never had any access to this paradise”. Her Son, our Lord Jesus Christ, would have it no other way.
Now, since bodily death is the consequence of sin (Romans 5:12), the question arises: If the Virgin Mary was exempted from the universal law of sin, would she also be exempt from having to suffer bodily death - especially since preservation from bodily death was one of the preternatural gift that Adam lost?
On November 1, 1950, in his Apostolic Constitution Munificentissimus Deus, Pope Pius XII defined, as an article of Faith, that the Blessed Virgin Mary was assumed bodily into heaven at the end of her life. He wrote: “ 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”.
The question of whether or not the Blessed Mother died before being assumed into heaven was specifically avoided in the definition, since the purpose was only to define the Assumption. He merely stated that she was assumed into heaven after “having completed the course of her earthly life”. In the same document, however, the Pope indicates, in numerous places, that the Blessed Mother did die before being assumed into heaven, and he cites multiple sources to support this belief. For example, he quotes the following from the sacramentary that Pope Adrian I sent to the Emperor Charlemagne: "Venerable to us, O Lord, is the festivity of this day on which the holy Mother of God suffered temporal death…”, as well as the Byzantine liturgy, which says: "God, the King of the universe, has granted you favors that surpass nature. As he kept you a virgin in childbirth, thus he has kept your body incorrupt in the tomb and has glorified it by his divine act of transferring it from the tomb." He also quotes St. Alphonsus, who wrote: “Jesus did not wish to have the body of Mary corrupted after death…”, and St. Francis De Sales, who asked: “What son would not bring his mother back to life and would not bring her into paradise after her death if he could?"
There is a solid tradition, in both the East and West, that the Blessed Mother suffered death before being assumed into heaven. In the eighth Century, St. John of Damascus (d. 749) formulated the tradition of the Church of Jerusalem as follows:
"St. Juvenal, Bishop of Jerusalem, at the Council of Chalcedon (451), made known to the Emperor Marcian and Pulcheria, who wished to possess the body of the Mother of God, that Mary died in the presence of all the Apostles, but that her tomb, when opened, upon the request of St. Thomas, was found empty; wherefrom the Apostles concluded that the body was taken up to heaven”.
In the Mystical City of God, Ven. Mary of Agreda recounts the same events as described above, but adds many more details, including a little-known privilege that was granted to the Blessed Mother. The events concerning the Transition of the Blessed Mother were revealed to her in detail: She saw Our Lord “descend from heaven on a throne of ineffable glory, accompanied by all the Saints and innumerable angels”. He spoke to her the following words: “My dearest Mother, whom I have chosen for my dwelling place, the hour is come in which thou art to pass from this life… into the glory of My Father and Mine, where thou shalt possess the throne prepared for thee at my right hand…. And since, by my power and as my Mother, I have caused thee to enter the world free and exempt from sin, therefore also death shall have no right or permission to touch thee at thy exit from this world. If thou wishest not to pass through it, come with Me now to partake of my glory, which thou hast merited”. The blessed Mother responded: “My Son and Lord… thou, who art my true God, hast suffered death without being obliged to do so; it is proper that, as I have followed Thee in life, so I follow Thee also in death”. The Lord approved of this request, and the Blessed Mother pronounced the same words as Our Lord when He expired on the cross – “Into thy hands, O Lord, I commend my Spirit” – then closed her eyes and expired. In the book The Glories of Mary, St. Alphonsus quotes Bernardine de Bustis as follows: “Mary, by a singular privilege granted to no other Saint, loved, and was always actually loving God, in every moment of her life, with such ardor that, as St. Bernard declares, it required a continued miracle to preserve her life in the midst of such flames” (pg 411). Interestingly, according to Ven. Mary of Agreda, it was the suspension of this miracle that resulted in her death. It was revealed to her that the Blessed Virgin Mary “died at the moment when the divine power suspended the assistance, which until then had counteracted the sensible ardors of her burning love of God. As soon as this miraculous assistance was withdrawn, the fire of her love consumed the life-humors of her heart and thus caused the cessation of her earthly existence.”
The Lord was so pleased with this final sacrifice of His mother, in choosing to follow Him in death, that He granted her a new privilege for the benefit of her spiritual children. The Blessed Mother explained this privilege in the following words spoken to Ven. Mary of Agreda:
"My daughter, besides what thou hast understood and written of my glorious Transition, I wish to inform thee of another privilege, which was conceded to me by my divine son in that hour. Thou hast already recorded, that the Lord offered me the choice of entering into beatific vision with or without passing through the portals of death. … I chose death freely in order to imitate and follow Him. … Since I had seen my Son and true God die, I would not have satisfied the love I owe Him, if I had refused death, and I would have left a great gap in my conformity to and my imitation of my Lord, the God-man, whereas He wished me to bear a great likeness to Him in His most sacred humanity. … Hence my choosing to die was so pleasing to Him, and my prudent love therein obliged Him to such an extent, that in return, He immediately conceded to me a singular favor for the benefit of the children of the Church… It was this, that all those devoted to me, who should call upon me at the hour of death, constituting me as their Advocate in memory of my happy Transition and of my desiring to imitate Him in death, shall be under my special protection in that hour, shall have me as a defense against the demons, as a help and protection, and shall be presented by me before the tribunal of His mercy and there experience my intercession. In consequence the Lord gave me a new power and commission and He promised to confer great helps of His grace for a good death and for a purer life on all those who, in veneration of this mystery of my precious death, should invoke my aid.”
This privilege, granted to the Blessed Virgin Mary, will be applied to those who call upon her at the hour of death, in memory of her happy Transition and the death she willed to endure. One way to remember this privilege, and thereby profit from it, is to form the habit of recalling it when saying the Forth Glorious Mystery of the Rosary (the Assumption). In addition to offering this decade for the grace of a holy death, we should offer it in honor of the privilege granted to the Blessed Mother, as a result of her holy death, asking for the grace to call upon her at the hour of our death; for “they are certainly saved and reign in heaven for whom the Queen of mercy intercedes” (Bl. Denis the Carthusian).
Most Holy Virgin Mary, Mother of God, my Mother and Advocate. In honor of thy glorious Transition and the death you willed to endure in imitation of thy Divine Son, and in honor of the privilege you received through your death, I beseech thee, that thou wouldst vouchsafe to assist me at the hour of my death, and present me to thy Divine Son, asking that He be merciful to me, as a favor to thee. And should I, in my final agony, forget to call upon thee, do thou, O Most Blessed Virgin Mary, remember this prayer, and do not forget to intercede for me. Amen.
 “Original sin is concupiscence, materially, but privation of original justice, formally”. (ST, II-II q. 83, a. 3)