Objection 1. It seems that sacramental grace confers nothing in addition to the grace of the virtues and gifts. For the grace of the virtues and gifts perfects the soul sufficiently, both in its essence and in its powers; as is clear from what was said in I-II, 110, 3,4. But grace is ordained to the perfecting of the soul. Therefore sacramental grace cannot confer anything in addition to the grace of the virtues and gifts.
Objection 2. Further, the soul's defects are caused by sin. But all sins are sufficiently removed by the grace of the virtues and gifts: because there is no sin that is not contrary to some virtue. Since, therefore, sacramental grace is ordained to the removal of the soul's defects, it cannot confer anything in addition to the grace of the virtues and gifts.
Objection 3. Further, every addition or subtraction of form varies the species (Metaph. viii). If, therefore, sacramental grace confers anything in addition to the grace of the virtues and gifts, it follows that it is called grace equivocally: and so we are none the wiser when it is said that the sacraments cause grace.
On the contrary, If sacramental grace confers nothing in addition to the grace of the virtues and gifts, it is useless to confer the sacraments on those who have the virtues and gifts. But there is nothing useless in God's works. Therefore it seems that sacramental grace confers something in addition to the grace of the virtues and gifts.
I answer that, As stated in I-II, 110, 3,4, grace, considered in itself, perfects the essence of the soul, in so far as it is a certain participated likeness of the Divine Nature. And just as the soul's powers flow from its essence, so from grace there flow certain perfections into the powers of the soul, which are called virtues and gifts, whereby the powers are perfected in reference to their actions. Now the sacraments are ordained unto certain special effects which are necessary in the Christian life: thus Baptism is ordained unto a certain spiritual regeneration, by which man dies to vice and becomes a member of Christ: which effect is something special in addition to the actions of the soul's powers: and the same holds true of the other sacraments. Consequently just as the virtues and gifts confer, in addition to grace commonly so called, a certain special perfection ordained to the powers' proper actions, so does sacramental grace confer, over and above grace commonly so called, and in addition to the virtues and gifts, a certain Divine assistance in obtaining the end of the sacrament. It is thus that sacramental grace confers something in addition to the grace of the virtues and gifts.
Reply to Objection 1. The grace of the virtues and gifts perfects the essence and powers of the soul sufficiently as regards ordinary conduct: but as regards certain special effects which are necessary in a Christian life, sacramental grace is needed.
Reply to Objection 2. Vices and sins are sufficiently removed by virtues and gifts, as to present and future time. in so far as they prevent man from sinning. But in regard to past sins, the acts of which are transitory whereas their guilt remains, man is provided with a special remedy in the sacraments.
Reply to Objection 3. Sacramental grace is compared to grace commonly so called, as species to genus. Wherefore just as it is not equivocal to use the term "animal" in its generic sense, and as applied to a man, so neither is it equivocal to speak of grace commonly so called and of sacramental grace.
Source: Summa Theologica (New Advent)