This singular privilege of the Mother of God was not defined in the Church until the 19th Century. But her eminent holiness has always been proclaimed. A feast for the Conception of the Mary has been in existence since the 7th Century. The High Middle Ages would look for the theological solution that reconciles the universality of salvation through Christ and the immaculate conception of the Virgin.
Beginning in 1477, Pope Sixtus IV ordered the feast and office of the Immaculate Conception of the Virgin Mary in Rome. The Council of Trent did not decide the question, but it specified that it did not include the Blessed Virgin in its teaching on original sin. And in 1616, Pope Paul V forbade teaching against the Immaculate Conception.
On December 8, 1854, Pope Pius IX proceeded to solemnly define the Immaculate Conception through the Papal Bull Ineffabilis Deus. It is worthwhile to note the scriptural texts on which the definition is based.
Genesis 3:15: “I will put enmities between thee and the woman, and thy seed and her seed: she shall crush thy head, and thou shalt lie in wait for her heel.” All of the commentators agree in saying that the woman referred to is the Virgin. This text thus announces Mary’s victory over the devil, which implies her exemption from all sin.
Luke 1:28: “Hail, full of grace, the Lord is with thee.” The Fathers of the Church hold that this fullness of grace is such that she is excluded from all sin.
The definition of the Bull Ineffabilis
The Bull dated December 8, 1854 explains it this way: “We declare, pronounce, and define that the doctrine which holds that the most Blessed Virgin Mary, in the first instance of her conception, by a singular grace and privilege granted by Almighty God, in view of the merits of Jesus Christ, the Savior of the human race, was preserved free from all stain of original sin, is a doctrine revealed by God and therefore to be believed firmly and constantly by all the faithful.”
“The first instance of her conception” means the moment of the union of the body with the rational soul.
“Singular privilege” exempts the Virgin from the common law: she was conceived according to the laws of nature, thus the effect is suspended for her.
“In view of the merits of Jesus Christ” : the Immaculate Conception proceeds from the merits of Christ, Our Lady is therefore truly redeemed by the Savior.
“All stain”: the fault as well as punishment due to sin, this is why the sufferings experienced by the Most Holy Virgin are not considered as punishment.
“Revealed”: it is therefore a dogma, although only implicitly contained in Revelation. It is therefore de fide that the Virgin Mary was preserved from all stain of the original fault.
Theology is pleased to find suitable reasons to explain the Immaculate Conception
By placing her in relation to Christ: the fact of Christ being born of a mother subjected to sin would be dishonorable.
In relation to the Holy Trinity: it would not be appropriate for a person having such proximity to the Holy Trinity to have lived even a few moments in a state of sin.
On the side of the Church:
*Our Lady is the first of the redeemed. She must have a supreme perfection among all the redeemed, which consists in redemption as a means of preservation, and not restoration.
*A mediator must not oppose one of the terms to be met. Now the Virgin is the Mediatrix of All Graces, a role that she exercises in dependence on Christ. She must therefore be without sin.
From the dogma of the Immaculate Conception flows the fact that Our Lady had grace from the first instant of her conception, because original sin is the privation of sanctifying grace.