"Before the foundation of the world, God chose us in Christ to be holy and spotless and to live through love in his presence.
This act of divine love and freedom, in our Catholic Faith, has been applied to Mary in a particular way: Chosen to be conceived immaculate, clothed from the first moment of her existence with the garment of salvation which her Son Jesus would win for us.
Adam and Eve abused the freedom that God had given them, in a sinfully foolish attempt to marginalize God, driving him to the margins of human existence. But Mary rejoiced in God and in the joy of her God-given freedom drew God back into the centre of human existence by accepting God's invitation to have her life centred in Christ. Mary was created with a freedom that ensured she would be at God's disposal when the time came to accept God's invitation to assume a special mission: to be the mother of Jesus.
The dogma of Mary's Immaculate Conception developed over the centuries but was not defined as a dogma of Catholic Faith until 1854, when Pope Pius IX defined it. This in no way implies that the Pope somehow "created" the doctrine. Rather, the definition was a conscious and loving appropriation by the Church of a part of the history of salvation held by Catholics throughout the ages.
Mary Immaculate, Mother of Jesus, intercede for us.