Falling from grace after receiving it happens. And happens again. And again.
1 Now, although grace is bestowed upon men by the aforesaid sacraments, they are not, for all that, rendered incapable of sin.
2 For gratuitous gifts are received in the soul as habitual dispositions; it is not always, then, that a man acts according to those gifts. Nothing stops him who has a habit from acting in accord with the habit or against it; thus, a grammarian can in accord with grammar speak rightly, or even against grammar speak awkwardly.
It is also like this with the habits of the moral virtues, for one who has the habit of justice can also act against justice. This is the case because the use of habits in us depends on the will, but the will is related to each of two opposites. Manifestly, then, he who receives gratuitous gifts can sin by acting against grace.
Notes Boy howdy, can I.
3 What is more, there can be no impeccability in a man unless there is immutability of will. But immutability of will does not become man except so far as he attains his ultimate end. For what renders the will immutable is its complete fulfillment, so that it has no way to turn away from that on which it is made firm. But the fulfillment of will is not proportioned to a man except as attaining his ultimate end, for, as long as something remains to be desired, the will has not been fulfilled. Thus, then, impeccability is not proper for a man before he arrives at the ultimate end. And this, to be sure, is not given man in the grace which is bestowed in the sacraments, because the sacraments are for man’s assistance along the road to the end. Therefore, no one is rendered impeccable from the grace received in the sacraments.
4 Furthermore, every sin comes about from a kind of ignorance. Thus, the Philosopher says that “every evil man is ignorant”; and we read in Proverbs (14:22): “They err that work evil.” Therefore, then, a man can be secure from sin in the will, only when his intellect is secure from ignorance and from error. But, manifestly, a man is not rendered immune from every ignorance and error by the grace received in the sacraments; for such is a man whose intellect is beholding that truth which is the certitude of all truths; and this very beholding is the ultimate end of man, as was shown in Book III. It is not, then, by the grace of the sacraments that man is rendered impeccable.
5 Again, to that change in a man which accords with malice and virtue much is contributed by that change which accords with the soul’s passions. For by a reason curbing and ordering the soul’s passions a man becomes virtuous or is preserved in virtue, but by a reason following the passions a man becomes vicious. So long, then, as a man can be altered in the soul’s passions, he can also be altered in vice and virtue. But alteration in the soul’s passions is not taken away by the grace conferred in the sacraments; it persists in a man as long as the soul is united to the body, which is capable of passion. Manifestly, then, the sacramental grace does not render a man impeccable.
6 There is more. It seems superfluous to warn those not to sin who cannot sin. But in the evangelical and apostolic teaching the faithful are so admonished, although they have already received the grace of the Holy Spirit through the sacraments, for we read in Hebrews (12:15): “Looking diligently, lest any man be wanting to the grace of God; lest any root of bitterness springing up do hinder”; and in Ephesians (4:30): “Grieve not the Holy Spirit of God whereby you are sealed”; and again: “He that thinks himself to stand, let him take heed lest he fall” (1 Cor. 10). Even the Apostle himself says of himself: “I chastise my body and bring it into subjection, lest perhaps when I have preached to others, I myself should become a castaway” (1 Cor. 9:27). Therefore, men are not rendered impeccable by the grace received in the sacraments.
7 This excludes the error of certain heretics who say that man, after he has received the grace of the Spirit, is unable to sin, and that, if he sins, he never had the grace of the Holy Spirit.
8 They take, however, as a prop for their error the saying of 1 Corinthians (13:8): “Charity never falls away.” And 1 John (3:6, 9) says: “Whosoever abides in Him sins not; and whosoever sins has not seen Him nor known Him.” And later on, more expressly: “Whosoever is born of God commits not sin; for His seed abides in him, and he cannot sin use he is born of God.”
9 But for establishing their proposition these texts are not effective. For one does not say: “charity never falls away” on the ground that he who has charity does not sometimes lose it, since the Apocalypse (2:4) says: “I have somewhat against you because you hast left your first charity.” But “charity never falls away” was said because, when all other gifts of the Holy Spirit (which essentially contain some imperfection—the spirit of prophecy, for example, and this kind of thing) “shall be made void…when that which is perfect is come” (1 Cor. 13:8, 10), then in that state of perfection charity shall abide.
10 But the remarks taken from the Epistle of John are said for this reason: The gifts of the Holy Spirit by which a man is adopted or born again as a son of God have of themselves power enough to be able to preserve a man without sin, and a man cannot sin who lives by those gifts. He can, for all that, act against them, and sin by departing from them. For “whosoever is born of God… cannot sin” was said just as though one should say that “the hot cannot cool.” What is hot, nevertheless, can be made cool, and then it will make cool. Or it was said as though one should say that “the just man does no unjust things”; namely, in so far as he is just.