Reply Obj. 2: When ingratitude is a venial sin it is not contrary to, but beside charity: since it does not destroy the habit of charity, but excludes some act thereof.
Reply Obj. 3: Seneca also says (De Benef. vii): "When we say that a man after conferring a favor should forget about it, it is a mistake to suppose that we mean him to shake off the recollection of a thing so very praiseworthy. When we say: He must not remember it, we mean that he must not publish it abroad and boast about it."
Reply Obj. 4: He that is unaware of a favor conferred on him is not ungrateful, if he fails to repay it, provided he be prepared to do so if he knew. It is nevertheless commendable at times that the object of a favor should remain in ignorance of it, both in order to avoid vainglory, as when Blessed Nicolas threw gold into a house secretly, wishing to avoid popularity: and because the kindness is all the greater through the benefactor wishing not to shame the person on whom he is conferring the favor. _______________________
FOURTH ARTICLE [II-II, Q. 107, Art. 4]
Whether Favors Should Be Withheld from the Ungrateful?
Objection 1: It seems that favors should withheld from the ungrateful. For it is written (Wis. 16:29): "The hope of the unthankful shall melt away as the winter's ice." But this hope would not melt away unless favors were withheld from him. Therefore favors should be withheld from the ungrateful.
Obj. 2: Further, no one should afford another an occasion of committing sin. But the ungrateful in receiving a favor is given an occasion of ingratitude. Therefore favors should not be bestowed on the ungrateful.
Obj. 3: Further, "By what things a man sinneth, by the same also he is tormented" (Wis. 11:17). Now he that is ungrateful when he receives a favor sins against the favor. Therefore he should be deprived of the favor.
On the contrary, It is written (Luke 6:35) that "the Highest . . . is kind to the unthankful, and to the evil." Now we should prove ourselves His children by imitating Him (Luke 6:36). Therefore we should not withhold favors from the ungrateful.
I answer that, There are two points to be considered with regard to an ungrateful person. The first is what he deserves to suffer and thus it is certain that he deserves to be deprived of our favor. The second is, what ought his benefactor to do? For in the first place he should not easily judge him to be ungrateful, since, as Seneca remarks (De Benef. iii), "a man is often grateful although he repays not," because perhaps he has not the means or the opportunity of repaying. Secondly, he should be inclined to turn his ungratefulness into gratitude, and if he does not achieve this by being kind to him once, he may by being so a second time. If, however, the more he repeats his favors, the more ungrateful and evil the other becomes, he should cease from bestowing his favors upon him.