The Immaculate Conception is the Catholic teaching that
Mary was conceived in the womb of her
mother, Anne, without Original Sin, as a unique gift to her, in preparation for being the Mother of God.
It does NOT refer to the virginal conception of
Jesus Christ in the womb of
Mary. Only TV land and people not intelligent enough to get their theological facts from sources other than
popular films use "Immaculate Conception" to refer to the conception of Christ.
The doctrine of the the Immaculate Conception is based on the assumption of St Augustine's notion of Original Sin, which teaches that all human beings, from the moment of their conception, carry the guilt and stain of the sins of the first human beings. It is from this guilt that
Mary is said to have been uniquely preserved.
As this notion of Original Sin isn't accepted by Orthodox or other Christians, the Catholic teaching of the Immaculate Conception is seen by them as the solution to a problem that doesn't exist.
