Reply Obj. 2: That which makes an animal live is inseparable from an animal, because it is its substantial form, viz. the soul: consequently a dead thing cannot become a living thing, and a living and a dead thing differ specifically. On the other hand that which gives faith its form, or makes it live, is not essential to faith. Hence there is no comparison.
Reply Obj. 3: Grace causes faith not only when faith begins anew to be in a man, but also as long as faith lasts. For it has been said above (I, Q. 104, A. 1; I-II, Q. 109, A. 9) that God is always working man's justification, even as the sun is always lighting up the air. Hence grace is not less effective when it comes to a believer than when it comes to an unbeliever: since it causes faith in both, in the former by confirming and perfecting it, in the latter by creating it anew.
We might also reply that it is accidental, namely on account of the disposition of the subject, that grace does not cause faith in one who has it already: just as, on the other hand, a second mortal sin does not take away grace from one who has already lost it through a previous mortal sin.
Reply Obj. 4: When living faith becomes lifeless, faith is not changed, but its subject, the soul, which at one time has faith without charity, and at another time, with charity. _______________________
FIFTH ARTICLE [II-II, Q. 4, Art. 5]
Whether Faith Is a Virtue?
Objection 1: It would seem that faith is not a virtue. For virtue is directed to the good, since "it is virtue that makes its subject good," as the Philosopher states (Ethic. ii, 6). But faith is directed to the true. Therefore faith is not a virtue.
Obj. 2: Further, infused virtue is more perfect than acquired virtue. Now faith, on account of its imperfection, is not placed among the acquired intellectual virtues, as the Philosopher states (Ethic. vi, 3). Much less, therefore, can it be considered an infused virtue.
Obj. 3: Further, living and lifeless faith are the same species, as stated above (A. 4). Now lifeless faith is not a virtue, since it is not connected with the other virtues. Therefore neither is living faith a virtue.
Obj. 4: Further, the gratuitous graces and the fruits are distinct from the virtues. But faith is numbered among the gratuitous graces (1 Cor. 12:9) and likewise among the fruits (Gal. 5:23). Therefore faith is not a virtue.