On December 8th, the Church observes the feast of the Immaculate Conception of the Blessed Virgin Mary. This feast celebrates the fact that Mary, the Mother of Jesus, in order to be a most perfect vessel for the Savior, was herself conceived without original sin. This original sin, described metaphorically in the book of Genesis, is the essential brokenness that comes with being human. It’s the fallen part of our nature that leads us into actual sin.
Although you can’t find direct reference to the Immaculate Conception in the scriptures, it is something that the Church has believed from its earliest centuries. The writings of the ancient Fathers of the Church make many references to the Immaculate Conception. The celebration of a feast day in honor of the Immaculate Conception began in 1708, when Pope Clement XI promulgated the document Commissi Nobis.
The Church received a formal declaration of the doctrine of the Immaculate Conception in the Constitution Ineffabilis Deus of December 8, 1854. In that document Pius IX pronounced and defined that the Blessed Virgin Mary “in the first instance of her conception, by a singular privilege and grace granted by God, in view of the merits of Jesus Christ, the Savior of the human race, was preserved exempt from all stain of original sin.”
The Church regards this feast as so important that December 8th is a Holy Day of Obligation, on which Catholics are obliged to participate in the sacred liturgy. This is particularly apropos in the United States, where Our Lady of the Immaculate Conception is our national patroness.