Mary needed a Redeemer to prevent her from contracting the stain.
[COLUMN 3] WHOLLY EXEMPT FROM THE LAW; MIRACULOUS CONCEPTION.
Springs from Adam materially, not seminally. (Q. 31, A. 1)
His body lay under neither guilt nor effects of original sin.
The body being entirely free, could not transmit the stain to His soul.
No preventive grace needed.
Jesus Christ contracted neither debt nor stain.
Jesus Christ is not redeemed, but the Redeemer.
It will thus be seen how accurately St. Thomas speaks of the "flesh" or body of our Blessed Lady. For it should be remembered that, according to St. Thomas, the human body is animated in succession by (1) a vegetative, (2) a sensitive, and (3) a rational soul. Hence his assertion that "the flesh of the Blessed Virgin was conceived in original sin" (Q. 14, A. 3, ad 1) means that the body of the Blessed Virgin, being descended from Adam both materially and seminally, contracted the bodily defects which are conveyed by seminal generation, and are the results of the privation of original justice (Q. 69, A. 4, ad 3). Before animation, therefore the body of the Blessed Virgin would not be infected with the guilt of original sin, because privation of grace can only be in that which is the subject of grace, viz. the rational soul. Nevertheless, before animation the body of the Blessed Virgin, being seminally descended from Adam, was such that it would have been the means of transmitting the taint of original sin to the rational soul at the very first instant of animation, unless the grace of the Redeemer intervened and sanctified her soul "in that self-same instant," thus redeeming her and preventing her from contracting the guilt of original sin.
Why, then, does St. Thomas say that because the Blessed Virgin was not sanctified before animation, therefore she could be sanctified only after animation?