I answer that, As stated above (Q. 7, AA. 9, 10, 12), the abundance of grace sanctifying Christ's soul flows from the very union of the Word, according to John 1:14: "We saw His glory . . . as it were of the Only-Begotten of the Father, full of grace and truth." For it has been shown above (Q. 33, AA. 2, 3) that in the first instant of conception, Christ's body was both animated and assumed by the Word of God. Consequently, in the first instant of His conception, Christ had the fulness of grace sanctifying His body and His soul.
Reply Obj. 1: The order set down by the Apostle in this passage refers to those who by advancing attain to the spiritual state. But the mystery of the Incarnation is considered as a condescension of the fulness of the Godhead into human nature rather than as the promotion of human nature, already existing, as it were, to the Godhead. Therefore in the man Christ there was perfection of spiritual life from the very beginning.
Reply Obj. 2: To be sanctified is to be made holy. Now something is made not only from its contrary, but also from that which is opposite to it, either by negation or by privation: thus white is made either from black or from not-white. We indeed from being sinners are made holy: so that our sanctification is a cleansing from sin. Whereas Christ, as man, was made holy, because He was not always thus sanctified by grace: yet He was not made holy from being a sinner, because He never sinned; but He was made holy from not-holy as man, not indeed by privation, as though He were at some time a man and not holy; but by negation—that is, when He was not man He had not human sanctity. Therefore at the same time He was made man and a holy man. For this reason the angel said (Luke 1:35): "The Holy which shall be born of thee." Which words Gregory expounds as follows (Moral. xviii): "In order to show the distinction between His holiness and ours, it is declared that He shall be born holy. For we, though we are made holy, yet are not born holy, because by the mere condition of a corruptible nature we are tied . . . But He alone is truly born holy who . . . was not conceived by the combining of carnal union."
Reply Obj. 3: The Father creates things through the Son, and the whole Trinity sanctifies men through the Man Christ, but not in the same way. For the Word of God has the same power and operation as God the Father: hence the Father does not work through the Son as an instrument, which is both mover and moved. Whereas the humanity of Christ is as the instrument of the Godhead, as stated above (Q. 7, A. 1, ad 3; Q. 8, A. 1, ad 1). Therefore Christ's humanity is both sanctified and sanctifier. _______________________
SECOND ARTICLE [III, Q. 34, Art. 2]
Whether Christ As Man Had the Use of Free-will in the First Instant of His Conception?
Objection 1: It would seem that Christ as man had not the use of free-will in the first instant of His conception. For a thing is, before it acts or operates. Now the use of free-will is an operation. Since, therefore, Christ's soul began to exist in the first instant of His conception, as was made clear above (Q. 33, A. 2), it seems impossible that He should have the use of free-will in the first instant of His conception.
Obj. 2: Further, the use of free-will consists in choice. But choice presupposes the deliberation of counsel: for the Philosopher says (Ethic. iii) that choice is "the desire of what has been previously the object of deliberation." Therefore it seems impossible that Christ should have had the use of free-will in the first instant of His conception.
Obj. 3: Further, the free-will is "a faculty of the will and reason," as stated in the First Part (Q. 83, A. 2, Obj. 2): consequently the use of free-will is an act of the will and the reason or intellect. But the act of the intellect presupposes an act of the senses; and this cannot exist without proper disposition of the organs—a condition which would seem impossible in the first instant of Christ's conception. Therefore it seems that Christ could not have the use of free-will at the first instant of His conception.
On the contrary, Augustine says in his book on the Trinity (Gregory: Regist. ix, Ep. 61): "As soon as the Word entered the womb, while retaining the reality of His Nature, He was made flesh, and a perfect man." But a perfect man has the use of free-will. Therefore Christ had the use of free-will in the first instant of His conception.