The Blessed Virgin Mary, the Mother of God, was conceived full of sanctifying grace and free of any stain of original sin. In Catholicism, this is called the [Immaculate Conception](https://christianity.stackexchange.com/q/14657/3941). She was conceived in this way through the merits of Jesus Christ: by His sacrifice, she was preserved from original sin.

Furthermore, and strictly owing to a special privilege from God, she lived a life entirely free from sin, and it seems that she could not have done so otherwise:

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> If any one say that man once justified can during his whole life avoid all sins, even venial ones, as the Church holds that the Blessed Virgin did by special privilege of God, let him be anathema."
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First, a minor clarification. By "special privilege", does that quotation mean the very fact that Mary was born without original sin, or is it a separate gift?

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I have heard of (or can imagine) some explanations for why Mary merited the reception of her graces, such as:

* because of her perfect devotion to the Lord, or because of a natural disposition to be perfectly devoted to the Lord.
* because she was chosen by God, and that is merit enough.
* because she was Mother of God, and no other woman could have been chosen in her place, since no other woman was Mary.
* we do not know, because this was never revealed.

But without the backing of what may be a fair bit of research, all of these options are idle speculation. According to the Catholic Church, why did God choose Mary, from all eternity, to be the Blessed Mother of His Son?