Objection 1. It would seem that deeds deadened by sin are not revived by Penance. Because just as past sins are remitted by subsequent Penance, so are deeds previously done in charity, deadened by subsequent sin. But sins remitted by Penance do not return, as stated above (88, 1,2). Therefore it seems that neither are dead deeds revived by charity.
Objection 2. Further, deeds are said to be deadened by comparison with animals who die, as stated above (Article 4). But a dead animal cannot be revived. Therefore neither can dead works be revived by Penance.
Objection 3. Further, deeds done in charity are deserving of glory according to the quantity of grace or charity. But sometimes man arises through Penance to lesser grace or charity. Therefore he does not receive glory according to the merit of his previous works; so that it seems that deeds deadened by sin are not revived.
On the contrary, on Joel 2:25, "I will restore to you the years, which the locust... hath eaten," a gloss says: "I will not suffer to perish the fruit which you lost when your soul was disturbed." But this fruit is the merit of good works which was lost through sin. Therefore meritorious deeds done before are revived by Penance.
I answer that, Some have said that meritorious works deadened by subsequent sin are not revived by the ensuing Penance, because they deemed such works to have passed away, so that they could not be revived. But that is no reason why they should not be revived: because they are conducive to eternal life (wherein their life consists) not only as actually existing, but also after they cease to exist actually, and as abiding in the Divine acceptance. Now, they abide thus, so far as they are concerned, even after they have been deadened by sin, because those works, according as they were done, will ever be acceptable to God and give joy to the saints, according to Apocalypse 3:11: "Hold fast that which thou hast, that no man take thy crown." That they fail in their efficacy to bring the man, who did them, to eternal life, is due to the impediment of the supervening sin whereby he is become unworthy of eternal life. But this impediment is removed by Penance, inasmuch as sins are taken away thereby. Hence it follows that deeds previously deadened, recover, through Penance, their efficacy in bringing him, who did them, to eternal life, and, in other words, they are revived. It is therefore evident that deadened works are revived by Penance.
Reply to Objection 1. The very works themselves of sin are removed by Penance, so that, by God's mercy, no further stain or debt of punishment is incurred on their account: on the other hand, works done in charity are not removed by God, since they abide in His acceptance, but they are hindered on the part of the man who does them; wherefore if this hindrance, on the part of the man who does those works, be removed, God on His side fulfills what those works deserved.
Reply to Objection 2. Deeds done in charity are not in themselves deadened, as explained above, but only with regard to a supervening impediment on the part of the man who does them. On the other hand, an animal dies in itself, through being deprived of the principle of life: so that the comparison fails.
Reply to Objection 3. He who, through Penance, arises to lesser charity, will receive the essential reward according to the degree of charity in which he is found. Yet he will have greater joy for the works he had done in his former charity, than for those which he did in his subsequent charity: and this joy belongs to the accidental reward.
Source: Summa Theologica (New Advent)