Immaculate ConceptionThe Immaculate Conception is a Catholic doctrine that the Virgin Mary was preserved by God from the transmission of original sin at the time of her own conception. It is not, as is popularly believed, another name for the doctrine of the virgin birth. Immaculate Conception was defined by Pope Pius IX in his constitution Ineffabilis Deus, published December 8, 1854 (the Feast of the Immaculate Conception).
The doctrine is generally not shared by either Eastern Christianity or by Protestantism, though for different reasons. Eastern Christianity does not share this doctrine because it does not share Catholicism's Augustinian view of original sin and total depravity, and consequently has no theological need for the doctrine. The doctrine is also not explicitly developed in its tradition, although there are numerous references in the Greek and Syrian Fathers to Mary's purity and sinlessness.
Protestantism rejects the doctrine because it is not explicitly spelled out in the Bible. They also argue that if Mary could be born without sin, there does not appear to be any need for Jesus to be incarnated and die to save humanity from sin. Catholics respond to this argument by pointing out that Mary's freedom from sin depended entirely on the grace of God, and that the saving merits of Christ were applied to her "in advance".