The Immaculate Conception, according to the teaching of the Catholic Church, is the conception of the Blessed Virgin Mary free from original sin by virtue of the foreseen merits of her son Jesus Christ. The Catholic Church teaches that Mary was conceived by normal biological means in the womb of her mother, Saint Anne, but God acted upon her soul, keeping it “immaculate”.
The Immaculate Conception is commonly confused with the Virgin Birth of Jesus. Jesus’s birth is covered by the Doctrine of Incarnation, while the Immaculate Conception deals with the conception of Mary, not that of her son.
Although the belief that Mary was sinless, or conceived with an immaculate soul, has been widely held since Late Antiquity, the doctrine was not dogmatically defined until 1854, by Pope Pius IX in his papal bull Ineffabilis Deus. The Catholic Church celebrates the Feast of the Immaculate Conception on December 8; in many Catholic countries, it is a holy day of obligation or patronal feast, and in some a national public holiday.
Original sin and actual (personal) sin
The defined dogma of the Immaculate Conception regards original sin only, saying that Mary was preserved from any stain (in Latin, macula or labes, the second of these two synonymous words being the one used in the formal definition). The proclaimed Roman Catholic dogma states, “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 Saviour of the human race, was preserved free from all stain of original sin.” Therefore, being always free from original sin, the doctrine teaches that from her conception Mary received the sanctifying grace that would normally come with baptism after birth.
The definition makes no declaration about the Church’s belief that the Blessed Virgin was sinless in the sense of freedom from actual or personal sin. However, the Church holds that Mary was also sinless personally, “free from all sin, original or personal”. The Council of Trent decreed: “If anyone shall say that a man once justified can sin no more, nor lose grace, and that therefore he who falls and sins was never truly justified; or, on the contrary, that throughout his whole life he can avoid all sins even venial sins, except by a special privilege of God, as the Church holds in regard to the Blessed Virgin: let him be anathema.”