2 “Bless the Lord, O my soul, and forget not all His rewards”. But the rewards of the Lord cannot be before your eyes unless your sins are before your eyes. Let not delight in past sin be before your eyes, but let the condemnation of sin be before your eyes: condemnation from you, forgiveness from God. For thus God rewards you, so that you may say, “How shall I reward the Lord for all His rewards unto me?” This it was that the martyrs considering (whose memory we are this day celebrating), and all the saints who have despised this life, and as you have heard in the Epistle of St.
John, laid down their lives for the brethren, which is the perfection of love, even as our Lord says: “Greater love has no man than this, that a man lay down his life for his friends:” this the holy martyrs, then, considering, despised their lives here, that they might find them there, following our Lord's words when He said, “He that loves his life, shall lose it; and he that loses his life for My sake, shall keep it unto life eternal.”...“Forget not,” he says, “all His rewards:” not awards, but “rewards.” For something else was due, and what was not due has been paid.
Whence also these words: “What,” he asks, “shall I reward the Lord for all His rewards unto me?” You have rewarded good with evil; He rewards evil with good. How have you, O man, rewarded your God with evil for good? You who has once been a blasphemer, and a persecutor, and injurious, hast rewarded blasphemies. For what good things? First, because you are: but a stone also is. Next, because you live, but a brute also lives. What reward will you give the Lord, for His having created you above all the cattle; and above all the fowls of the air, in His image and likeness? Seek not how to reward Him: give back unto Him His own image: He requires no more; He demands His own coin....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)