The Roman Catholic Church celebrates the Solemnity of the Immaculate Conception of the Virgin Mary on December 8. It is a feast that recognizes Mary's conception without any stain of sin.
While not explicitly mentioned in the Bible, the dogma of the Immaculate Conception is supported by various scripture passages.
Full of grace
In the Gospel of Luke, Mary is called “full of grace,” a term that reflects her “immaculate” (from the Latin for “without stain”) state.
And he came to her and said, “Hail, full of grace, the Lord is with you!”
The Catechism of the Catholic Church explains this connection.
Through the centuries the Church has become ever more aware that Mary, “full of grace” through God, was redeemed from the moment of her conception. That is what the dogma of the Immaculate Conception confesses, as Pope Pius IX proclaimed in 1854. The most Blessed Virgin Mary was, from the first moment of her conception, by a singular grace and privilege of almighty God and by virtue of the merits of Jesus Christ, Savior of the human race, preserved immune from all stain of original sin.
The single verse from Luke is the most direct affirmation from the Bible that Mary was immaculately conceived.