Was the Blessed Virgin conceived in sin? The answer is no, for as Augustine writes: "When sin is treated, there can be no inclusion of Mary in the discussion." And Anselm says: "It was fitting that the Virgin should be resplendent with a purity greater than which none under God can be conceived." Purity here is to be taken in the sense of pure innocence under God, such as was in Christ.
The contrary, however, is commonly asserted on two grounds. First, the dignity of her Son, who, as universal Redeemer, opened the gates of heaven. But if Blessed Mary had not contracted original sin, she would not have needed the Redeemer, nor would He have opened the door for Her because it was never closed. For it is only closed because of sin, above all original sin.
In respect to this first ground, one can argue from the dignity of her Son as Redeemer, Reconciler, and Mediator, that she did not contract original sin.
For a most perfect mediator exercises the most perfect mediation possible in regard to some person for whom he mediates. Thus Christ exercised a most perfect act of mediation in regard to some person for whom He was Mediator. In regard to no person did He have a more exalted relationship than to Mary. Such, however, would not have been true had He not preserved her from original sin.
Blessed John Duns Scotus
Ordinatio II, d. 3, q. 1
Ordinatio II, d. 3, q. 1
