6 “For Thou, Lord, hast made me glad through Your works; and I will rejoice in giving praise for the operations of Your hands”. You see what he says. You have made me living well, You have formed me: if by chance I do anything of good, I will rejoice in the work of Your hands: as the Apostle says, “For we are His workmanship, created unto good works.” For unless He formed you to good works, you would not know any works but evil....Because you can not have truth from your own self, it remains that thou drink it thence, whence it flows: as if you have gone back from the light, you are in darkness: as a stone glows not with its own heat, but either from the sun or fire, and if you withdraw it from the heat, it cools: there it appears, that the heat was not its own; for it became heated either by the sun or by fire: thus thou also, if you withdraw from God, wilt become cold; if you approach God, you will warm: as the Apostle says “fervent in spirit.” Also what says he of the light?
If you approach Him, you will be in light; therefore says the Psalm, “Look upon Him, and be lightened; and your faces shall not be ashamed.” Because therefore you can do no good, unless lightened by the light of God, and warmed by the spirit of God; when you shall see yourself working well, confess unto God, and say what the Apostle says; say unto yourself, that you be not puffed up, “For what have you that thou did not receive?”...
Source: The Enarrations, or Expositions, on the Psalms (New Advent)