7 Wherefore it is necessary to forget our good actions. “Yet how is it possible,” one may say, “not to know these things with which we are well acquainted?” How do you say? Offending your Lord perpetually, you live delicately, and laughest, and dost not so much as know that you have sinned, but hast consigned all to oblivion; and of your good actions can you not put away the memory? And yet fear is a stronger kind of thing. But we do the very contrary; on the one hand, while each day we are offending, we do not so much as put it before our mind; on the other, if we give a little money to a poor person, this we are ever revolving. This kind of conduct comes of utter madness, and it is a very great loss to him who so makes his reckoning. For the secure storehouse of good works is to forget our good works. And as with regard to raiment and gold, when we expose them in a market-place, we attract many ill-meaning persons; but if we put them by at home and hide them, we shall deposit them all in security: even so with respect to our good deeds; if we are continually keeping them in memory, we provoke the Lord, we arm the enemy, we invite him to steal them away; but if no one know of them, besides Him who alone ought to know, they will lie in safety.
Be not therefore for ever parading them, lest some one should take them away. As was the case with the Pharisee, for bearing them about upon his lips; whence also the devil caught them away. And yet it was with thanksgiving he made mention of them, and referred the whole to God. But not even did this suffice Him. For it is not thanksgiving to revile others, to be vainglorious before many, to exalt one's self against them that have offended. Rather, if you are giving thanks to God, be content with Him only, and publish it not unto men, neither condemn your neighbor; for this is not thanksgiving. Would you learn words of thanksgiving? Hearken unto the Three Children, saying, “We have sinned, we have transgressed. You are righteous, O Lord, in all that you have done unto us, because you have brought all things upon us by a true judgment.” For to confess one's own sins, this is to give thanks with confession unto God: a kind of thing which implies one to be guilty of numberless offenses, yet not to have the due penalty exacted. This man most of all is the giver of thanks.
Source: Homilies on the Gospel of St. Matthew (New Advent)