Today the Church celebrates the Solemnity of the Immaculate Conception, the solemn dogma defined by Blessed Pope Pius IX in 1854. As Our Lady Immaculately Conceived is the patroness of the United States of America, this is a holy day of obligation in the United States.
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 Blessed Pope Pius IX proclaimed on December 8, 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, Saviour of the human race, preserved immune from all stain of original sin." — Catechism of the Catholic Church