From Archbishop Fulton J. Sheen's The World's First Love: Mary, Mother of God:
God never does anything without exceeding preparation. The two great masterpieces of God are Creation of man and Re-creation or Redemption of man. Creation was made for unfallen men; His Mystical Body, for fallen men. Before making man, God made a garden of delights—as God alone knows how to make a garden beautiful. In that Paradise of Creation there were celebrated the first nuptials of man and woman. But man willed not to have blessings, except according to his lower nature. Not only did he lose his happiness; he even wounded his own mind and will. Then God planned the remaking or redeeming of man. But before doing so, he would make another Garden. This new one would be not of earth but of flesh; it would be a Garden over whose portals the name of sin would never be written—a Garden in which there would grow no weeds of rebellion to choke the growth of the flowers of grace—a Garden from which there would flow four rivers of redemption to the four corners of the earth—a Garden so pure that the Heavenly Father would not blush at sending His Own Son into it—and this "flesh-girt Paradise to be gardened by the Adam new" was Our Blessed Mother. As Eden was the Paradise of Creation, Mary is the Paradise of the Incarnation, and in her as a Garden were celebrated the first nuptials of God and man. The closer one gets to fire, the greater the heat; the closer one is to God, the greater the purity. But since no one was ever closer to God than the woman whose human portals He threw open to walk this earth, then no one could have been more pure than she. In the words of Lawrence Housman:
A garden bower in flower
Grew waiting for God's hand:
Where no man ever trod,
This was the Gate of God.
The first bower was red—
Her lips which "welcome" said.
The second bower was blue—
Her eyes that let God through.
The third bower was white—
Her soul in God's sight.
Three bowers of love
Now Christ from heaven above.
This special purity of hers we call the Immaculate Conception. It is not the Virgin Birth. The word "immaculate" is taken from two Latin words meaning "not stained." "Conception" means that, at the first moment of her conception, the Blessed Mother in the womb of her mother, St. Anne, and in virtue of the anticipated merits of the Redemption of her Son, was preserved free from the stains of Original Sin.
I never could see why anyone in this day and age should object to the Immaculate Conception; all modern pagans believe that they are immaculately conceived. If there is no Original Sin, then everyone is immaculately conceived. Why do they shrink from allowing to Mary what they attribute to themselves? The doctrine of Original Sin and the Immaculate Conception are mutually exclusive. If Mary alone is the Immaculate Conception, then the rest of us must have Original Sin.
The Immaculate Conception does not imply that Mary needed no Redemption. She needed it as much as you and I do. She was redeemed in advance, by way of prevention, in both body and soul, in the first instant of conception. We receive the fruits of redemption in our soul at Baptism. The whole human race needs redemption. But Mary was de-solidarized and separated from that sin-laden humanity as a result of the merits of Our Lord's Cross being offered to her at the moment of her conception. If we exempted her from the need of redemption, we would also have to exempt her from membership in humanity. The Immaculate Conception, therefore, in no way implies that she needed no redemption. She did! Mary is the first effect of redemption, in the sense that it was applied to her at the moment of her conception and to us in another and diminished fashion only after our birth.
She had this privilege, not for her sake, but for His sake. That is why those who do not believe in the Divinity of Christ can see no reason for the special privilege accorded to Mary. If I did not believe in the Divinity of Our Lord—which God avert—I should see nothing but nonsense in any special reverence given to Mary above the other women on earth! But if she is the Mother of God, Who became Man, then she is unique, and then she stands out as the new Eve of Humanity—as He is the new Adam.