The solemn definition of Mary’s Immaculate Conception was proclaimed as an independent dogma by Blessed Pope Pius IX in his Apostolic Constitution “Ineffabilis Deus” (December 8, 1854). Though the Holy Father was highlighting a privilege given to Blessed Mother, in fact he was also stressing the particular dignity and holiness that was required to become “Mother of God.” Since Christ Himself is sinless, so also this privilege was according to His Mother so that the human nature, which Christ received from her would not be tainted by original sin.
The dogma of the Immaculate Conception states “that the most Blessed Virgin Mary, from the first moment of her conception, by a singular grace and privilege from Almighty God and in view of the merits of Jesus Christ, was kept free of every stain of original sin.” This teaching stresses that Mary’s freedom from original sin was a privilege afforded to her prior to the suffering, death and resurrection of Christ, and yet this freedom was still dependent upon it. Christ suffered and died for the redemption of our sins. This dogma says that Mary shared in the graces of the Paschal Mystery in an anticipated or retroactive way.
Although difficult to explain, original sin brings about disorder in thought and behavior. While original sin is taken away with Baptism, the effects of this sin remain. Our Lady was preserved from Original Sin and hence also from its effects. Her human nature was preserved from any disorder or disintegration caused by sin. In declaring Our Lady “immaculately conceived," the Church sees in Mary one who never denied God the least sign of love. Thus, the dogma declares that from her very beginning Mary was exceptionally holy and in constant union with the sanctifying grace of the Holy Spirit. Immaculate Heart of Mary, pray for us, that we may love the Lord as you have loved Him.