And thus, even as the natural light of reason is something besides the acquired virtues, which are ordained to this natural light, so also the light of grace which is a participation of the Divine Nature is something besides the infused virtues which are derived from and are ordained to this light, hence the Apostle says (Eph. 5:8):  “For you were heretofore darkness, but now light in the Lord.  Walk then as children of the light.”  For as the acquired virtues enable a man to walk, in accordance with the natural light of reason, so do the infused virtues enable a man to walk as befits the light of grace.

Reply Obj. 1:  Augustine calls “faith that worketh by charity” grace, since the act of faith of him that worketh by charity is the first act by which sanctifying grace is manifested.

Reply Obj. 2:  Good is placed in the definition of virtue with reference to its fitness with some pre-existing nature essential or participated.  Now good is not attributed to grace in this manner, but as to the root of goodness in man, as stated above.

Reply Obj. 3:  Grace is reduced to the first species of quality; and yet it is not the same as virtue, but is a certain disposition which is presupposed to the infused virtues, as their principle and root. ________________________

FOURTH ARTICLE [I-II, Q. 110, Art. 4]

Whether Grace Is in the Essence of the Soul As in a Subject, or in
One of the Powers?

Objection 1:  It would seem that grace is not in the essence of the soul, as in a subject, but in one of the powers.  For Augustine says (Hypognosticon iii [Among the spurious works of St. Augustine]) that grace is related to the will or to the free will “as a rider to his horse.”  Now the will or the free will is a power, as stated above (I, Q. 83, A. 2).  Hence grace is in a power of the soul, as in a subject.

Obj. 2:  Further, “Man’s merit springs from grace” as Augustine says (De Gratia et Lib.  Arbit. vi).  Now merit consists in acts, which proceed from a power.  Hence it seems that grace is a perfection of a power of the soul.

Obj. 3:  Further, if the essence of the soul is the proper subject of grace, the soul, inasmuch as it has an essence, must be capable of grace.  But this is false; since it would follow that every soul would be capable of grace.  Therefore the essence of the soul is not the proper subject of grace.

Obj. 4:  Further, the essence of the soul is prior to its powers.  Now what is prior may be understood without what is posterior.  Hence it follows that grace may be taken to be in the soul, although we suppose no part or power of the soul—­viz. neither the will, nor the intellect, nor anything else; which is impossible.

On the contrary, By grace we are born again sons of God.  But generation terminates at the essence prior to the powers.  Therefore grace is in the soul’s essence prior to being in the powers.