The Feast of the Immaculate Conception celebrates the solemn celebration by various Christian denominations of belief in the Immaculate Conception of the Blessed Virgin Mary.
Why is it important?
Immaculate Conception is a Roman Catholic dogma asserting that Mary, the mother of Jesus, was preserved free from the effects of the sin of Adam (usually referred to as "original sin") from the first instant of her conception.
First debated by medieval theologians, it proved so controversial that it did not become part of official Catholic teaching until 1854, when Pius IX gave it the status of dogma in the papal bull Ineffabilis Deus.
The feast day of the Immaculate Conception is December 8 and is usually a holy day of obligation (on which Catholics are required to attend mass).