1. Response

41. About the third main article [n.9] I say that sin dismissed returns as a circumstance worsening the sin by which the sinner fell back.

42. And this in two ways:

First, because the more someone receives from another a benefit that is more undue to him, the more is he bound to that other by the law of gratitude - even if the benefit received be less undue, and consequently more if the benefit received be equally undue. But to someone existing in sin God owes nothing save a penalty; therefore, if God confer grace on him, this will be a gift most gratuitously and liberally conferred, and especially if the grace is equal to the grace of the innocent. Therefore, by the law of gratitude he is, because of this freely conferred gift, especially obligated to God - and consequently, when offending afterwards against him, he sins, because of the ingratitude, more gravely.

43. Second, because the more someone is bound to something by more obligations, the more, if he transgresses, does he sin more gravely. But a penitent, as often as he is worthily penitent, obligates himself, at least in desire, to not committing sin in the future, because without such purpose the penitence is not worthy; and besides this, he is constrained to not committing sin by the same law as that by which the innocent is constrained. Therefore, if he sins afterwards, he transgresses a double law obligating him to not committing transgression, namely both the general one [sc. not to sin] and this special one about keeping a promise [sc. the promise made in penitence], which obligates most of all as to a promise made to God, and as to something that pertains to the honor of God.