6 “Behold” (you say), “I do long after it, I do ask for it, I do desire it. Shall I then accomplish it?” No. Who shall then? “Reveal your way unto the Lord: trust also in Him, and He shall bring it to pass”. Mention to Him what you suffer, mention to Him what thou dost desire. For what is it that you suffer? “The flesh lusts against the spirit, and the spirit against the flesh.” What is it then that you desire? “Wretched man that I am! Who shall deliver me from the body of this death?” And because it is He “Himself” that “will bring it to pass,” when you shall have “revealed your ways unto Him;” hear what follows: “The grace of God through Jesus Christ our Lord.” What is it then that He is to bring to pass, since it is said, “Reveal your way unto Him, and He will bring it to pass”? What will He bring to pass?
“And He shall bring forth your righteousness as the light”. For now, “your righteousness” is hid. Now it is a thing of faith; not yet of sight. You believe something that you may do it. You do not yet see that in which you believe. But when you shall begin to see that, which you believed before, “your righteousness will be brought forth to the light,” because it is your faith that was your righteousness. For “the just lives by faith.”
Source: The Enarrations, or Expositions, on the Psalms (New Advent)