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.
12. “For the Lord shall give sweetness, and our land shall give her increase”....He will give unto you the sweetness of working righteousness, so that righteousness shall begin to delight you, whom before unrighteousness delighted: so that thou who at first delighted in drunkenness, shall rejoice in sobriety: and thou who at first rejoiced in theft, so as to take from another man what you had not, shall seek to give to him that has not that which you have: and thou who took delight in robbing, shall delight now in giving: thou whom shows delighted, shall delight in prayer; thou who delighted in trifling and lascivious songs, shall now delight in singing hymns to God; in running to church, thou who at first ran to the theatre. Whence is that sweetness born to you, except from this, that “God gives sweetness”? For, behold, you see what I mean: behold, I have spoken unto you the word of God, I have sown seed in your devout hearts, finding your souls furrowed, as it were, with the plough of confession: with devout attention you have received the seed; think now upon the word which you have heard, like those who break up the clouds, lest the fowls should carry away the seed, that what is sown may be able to spring up there: and unless God rain upon it, what profits it that it is sown? This is what is meant by “our land shall give her increase.” May He with His visitations, in leisure, in business, in your house, in your bed, at meal-time, in conversation, in walks, visit your hearts, when we are not by. May the rain of God come and make to sprout what is sown there: and when we are not by, and are resting quietly, or otherwise employed, may God give increase to the seeds which we have sown, that remarking afterwards your improved characters, we too may rejoice for your fruit.
13. “For righteousness shall go before him, and he shall direct his steps in the way”: that righteousness, namely, which consists in confession of sins: for this is truth itself. For you ought to be righteous towards yourself, and to punish yourself: for this is the beginning of man's righteousness, that you should punish yourself, who art evil, and God should make you good. Therefore since this is the beginning of man's righteousness, this becomes a way for God, that God may come unto you: there make for Him a way, in confession of sins. Therefore John too, when he was baptizing in the water of repentance, and would have men come to him repenting of their former deeds, spoke thus: “Prepare the way of the Lord, make His paths straight.” You pleased yourself in your sins, O man: let that which you were displease you, that you may be able to become what you were not. Prepare the way of the Lord: let that righteousness go before, of confession of sins: He will come and visit you, for now He has where to place His steps, He has whereby He may come to you. Before you confessed your sins, you had shut up the way of God: there was no way by which He might come unto you. Confess your past life, and you open a way; and Christ shall come unto you, and “shall place His steps in the way,” that He may guide you with His own footsteps.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)