2 Let my limbs, he says, serve the Lord: I speak, but it is of Yours I speak. “With my mouth will I make known Your truth:” if I obey not You, I am not Your servant: if I speak on my own part, I am a liar. To speak then from You, and in my own person, are two things: one mine, one Yours: Truth Yours, language mine. Let us hear then what faithfulness he makes known, what mercies he sings.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)