Thomas Aquinas

“ One human act does not remove all the remnants of sin, because, as stated in the Predicaments (Categor. viii) "a vicious man by doing good works will make but little progress so as to be any better, but if he continue in good practice, he will end in being good as to acquired virtue." But God's grace does this much more effectively, whether by one or by several acts. ”

“ Art. 6 - Whether the forgiveness of guilt is an effect of Penance? Objection 1: It would seem that the forgiveness of guilt is not an effect of penance as a virtue. For penance is said to be a virtue, in so far as it is a principle of a human action. But human action does nothing towards the remission of guilt, since this is an effect of operating grace. Therefore the forgiveness of guilt is not an effect of penance as a virtue.
Objection 2: Further, certain other virtues are more excellent than penance. But the forgiveness of sin is not said to be the effect of any other virtue. ”

“ Now there is nothing to hinder God from loving a man in one respect, while being offended with him in another, even as He loves the sinner as regards his nature, while hating him for his sin. Therefore it seems possible for God, by Penance, to pardon one sin without another. ”

“ But Penance is a sacrament. Therefore by God's power sin can be pardoned without Penance.
Objection 3: Further, God's mercy is greater than man's. Now man sometimes forgives another for offending him, without his repenting: wherefore our Lord commanded us (Mat. 5:44) : "Love your enemies, do good to them that hate you." Much more, therefore, does God pardon men for offending him, without their repenting. ”

“ These words of Augustine should be understood thus: "So great is the stain of that sin, that man is unable to humble himself in prayer," i.e. it is not easy for him to do so; in which sense we say that a man cannot be healed, when it is difficult to heal him. ”

“ When a man who hates his neighbor, breaks himself of other vices, rain falls on one part of the city, leaving the other part withered, for there are some men who, when they prune some vices, become much more rooted in others. ”

“ Consequently such Penance brings no hope of pardon, but only despair. Nevertheless no sin of a wayfarer can be such as that, because his will is flexible to good and evil. Wherefore to say that in this life there is any sin of which one cannot repent, is erroneous, first, because this would destroy free-will, secondly, because this would be derogatory to the power of grace, whereby the heart of any sinner whatsoever can be moved to repent, according to Prov. ”