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)