Thomas Aquinas

“ Now it is evident that there is a special reason for praising the act of penance, because it aims at the destruction of past sin, considered as an offense against God, which does not apply to any other virtue. We must therefore conclude that penance is a special virtue.
Reply to Objection 1: An act springs from charity in two ways: first as being elicited by charity, and a like virtuous act requires no other virtue than charity, e.g. to love the good, to rejoice therein, and to grieve for what is opposed to it. Secondly, an act springs from charity, being, so to speak, commanded by charity ”

“ Because shame regards the evil deed as present, whereas penance regards the evil deed as past. Now it is contrary to the perfection of virtue that one should have an evil deed actually present, of which one ought to be ashamed; whereas it is not contrary to the perfection of virtue that we should have previously committed evil deeds, of which it behooves us to repent, since a man from being wicked becomes virtuous. ”

“ As there is a kind of commutation in favors, when, to wit, a man gives thanks for a favor received, so also is there commutation in the matter of offenses, when, on account of an offense committed against another, a man is either punished against his will, which pertains to vindictive justice, or makes amends of his own accord, which belongs to penance, which regards the person of the sinner, just as vindictive justice regards the person of the judge. ”

“ Sin begins to displease a man, especially a sinner, on account of the punishments which servile fear regards, before it displeases him on account of its being an offense against God, or on account of its wickedness, which pertains to charity. ”

“ A thing is just simply when it is between equals, since justice is a kind of equality, and he calls this the politic or civil just, because all citizens are equal, in the point of being immediately under the ruler, retaining their freedom. But a thing is just relatively when it is between parties of whom one is subject to the other, as a servant under his master, a son under his father, a wife under her husband. It is this kind of just that we consider in penance. Wherefore the penitent has recourse to God with a purpose of amendment, as a servant to his master, according to Ps. ”

“ When the kingdom of heaven is said to be at hand, we are to understand that the king is on his way, not only to reward but also to punish. Wherefore John the Baptist said (Mat. 3:7) : "Ye brood of vipers, who hath showed you to flee from the wrath to come?" ”