Thomas Aquinas

“ These scourges always regard past guilt, not always the guilt of the person, but sometimes the guilt of nature. For had there not been guilt in human nature, there would have been no punishment. But since guilt preceded in nature, punishment is inflicted by God on a person without the person's fault, that his virtue may be meritorious, and that he may avoid future sin. Moreover, these two things are necessary in satisfaction. For the work needs to be meritorious, that honor may be given to God, and it must be a safeguard of virtue, that we may be preserved from future sins. ”

“ Although each of these three, by a kind of likeness, is appropriated to some particular kind of sin because it is reasonable that, whereby a man sins, in that he should be punished, and that satisfaction should cut out the very root of the sin committed, yet each of them can satisfy for any kind of sin. Hence if a man is unable to perform one of the above, another is imposed on him, chiefly almsdeeds, which can take the place of the others, in so far as in those to whom a man gives alms he purchases other works of satisfaction thereby. ”

“ Although these scourges are not altogether in our power, yet in some respect they are, in so far as we use them patiently. In this way man makes a virtue of necessity, so that such things can become both meritorious and satisfactory.
Reply to Objection 2: As Augustine observes (De Civ. Dei i, 8) , even as "the same fire makes gold glisten and straw reek," so by the same scourges are the good cleansed and the wicked worsened on account of their impatience. Hence, though the scourges are common to both, satisfaction is only on the side of the good. ”