What is the Immaculate Conception?
The Immaculate Conception refers to the dogma that the Blessed Virgin Mary was conceived without any stain of Original Sin in preparation for becoming the Mother of God, the Son Jesus Christ.
Before the creation of the world, God the Father chose the Blessed Virgin Mary to be the Mother of his Son, Jesus Christ. The Archangel Gabriel announced to her that she was “full of grace” (Luke 1:29)—or God’s “favored one,” as in some Scripture translations—indicating her unique worthiness to conceive the Son of God; she “was enriched by God with the gifts which befit such a role” (LG 56). From the very beginning the Church has believed not only that the Blessed Virgin Mary was a virgin but also that she was not conceived with any stain of Original Sin into which everyone is conceived after the sin of Adam and Eve. This unique privilege enabled her to fulfill perfectly her unique mission as the Mother of God. God the Father blessed the Mother of his Son more than any other created person “in Christ with every spiritual blessing in the heavenly places [and chose her] in Christ before the foundation of the world, to be holy and blameless before him in love” (Bl. Pius IX, Ineffabilis Deus [1854]: DS 2803). (Cf. CCC 966)
The Church has celebrated the Immaculate Conception of the Blessed Virgin Mary with a feast since perhaps as early as the fifth century, and it was made a Holy Day of Obligation in 1708.