The Immaculate Conception means that God in his infinite wisdom created a woman, Mary, who from the first moment of her conception was free from Original Sin.
This means that God so loves her above all angels and saints bestowing on her fullness of innocence and sanctity so great that outside of God, no human mind can understand fully this mystery. (Encyclical,Ineffabilis Deus: Pope Pius IX)
This implies a freedom from those tendencies of fallen human nature to disfigure one's spiritual focus upon God and his will. She was freed from pride, that is, too great an admiration of herself, avarice or the desire for wealth as an end in itself, envy of others, lust or the inordinate desire for sexual pleasure, anger as a a violent desire to punish others, gluttony , the abuse of the pleasure associated with eating and drinking, and sloth or laziness both spiritual and physical which leads to neglect one's duties in life.
In Mary was fulfilled the ancient prophecy of Genesis 3:15 "I will put enmity between you and the woman, and between your offspring and hers; He will strike at your head, while you strike at his heel." (Gn 3:15) This is why Mary is depicted crushing the head of the Serpent. Satan has no claim on Mary and the Son of God she was destined to bring into the world is indeed continually casting out the Prince of Darkness.|
Pope Pius IX defined the Immaculate Conception as a truth of faith on December 8, 1854, yet c. 1750 St. Alphonsus Liguori wrote a remarkable prayer:
O Immaculate Mary!
I rejoice with you on seeing you enriched with such great purity. I thank God, and resolve always to thank Him for having preserved you from every stain of sin. I firmly believe this doctrine and am willing to lay down my life - St. Alphonsus Liguor and even swear to do so if this be necessary - in defense of this great and unique privilege, the privilege of your Immaculate Conception....
Mother of God