Thomas Aquinas

“ Although sins, when committed, were voluntary, yet when we are contrite for them, they are no longer voluntary, so that they occur against our will; not indeed in respect of the will that we had when we consented to them, but in respect of that which we have now, so as to wish they had never been. ”

“ And since, for the remission of sin, it is necessary that man should put aside entirely his attachment to sin, which implies a certain state of continuity and solidity in his mind, therefore it is that the act through which sin is cast aside is called contrition metaphorically. ”

“ It may also be replied that matter does not take its origin from the form essentially, as an act takes its origin from the habit which quickens it. Wherefore nothing hinders matter being quickened anew by some form, whereby it was not quickened previously: whereas this cannot be said of an act, even as it is impossible for the identically same thing to arise from a cause wherefrom it did not arise before, since a thing is brought into being but once. ”

“ For just as the inflation of one's own will unto wrong-doing implies, in itself, a generic evil, so the utter undoing and crushing of that same will implies something generically good, for this is to detest one's own will whereby sin was committed. Wherefore contrition, which signifies this, implies rectitude of the will; and so it is the act of that virtue to which it belongs to detest and destroy past sins, the act, to wit, of penance, as is evident from what was said above (Sent. iv, D, 14, Q [1] , A [1] ; [4821] TP, Q [85] , AA [2] ,3) . ”