On the Solemnity of the Immaculate Conception…

Today is the Feast of the Immaculate Conception. What does that mean? According to Pope Pius IX, Mary was given grace to be sinless at the instant of her conception:
“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.” (Pius IX, Ineffabilis Deus, 1854)