11 On the same passage we may mention another meaning. “Truth is sprung out of the earth:” confession from man. For thou, O man, wast a sinner. O earth, who when you had sinned heard the sentence, “Earth you are, and unto earth shall you return,” from you let truth spring, that righteousness may look down from heaven. How does truth spring from you, while you are a sinner, while you are unrighteous? Confess your sins, and truth shall spring out of you. For if while you are unrighteous, you call yourself just, how can truth spring out of you? But if being unrighteous thou dost confess yourself to be so, “truth has sprung out of the earth.”...What “righteousness has looked down from heaven”? It is that of God, as though He said: Let us spare this man, for he spares not himself: let us pardon him, for he himself confesses. He is changed so as to punish his sin: I too will change, so as to set him free.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)