Augustine of Hippo

"I acknowledged my sin, and my unrighteousness have I not hid:" that is, my unrighteousness have I not concealed. "I said, I will confess against myself my unrighteousness to the Lord:" I said, I will confess, not against God (as in my ungodly crying, when I kept silence), but against myself, my unrighteousness to the Lord. "And Thou forgavest the iniquity of my heart" [Psalm 32:5]; hearing the word of confession in the heart, before it was uttered with the voice.

Exposition on Psalm 32 ↗

Thomas Aquinas

Then when he says "My offense." First, he sets forth the confession. Second, he shows its efficacy, at "I said, I will confess." But because a person ought to confess two things, namely, good things omitted and evil things committed, as to the first he says, "My offense," namely, that I omitted doing what I should have done, "I have made known to you" -- not that God does not know, but when a person acknowledges his sin, then he also wants God to know it, so that he may pardon it. …

Exposition on the Psalms of David ↗

Bonaventure

Piety avails for avoiding all evils. Do you wish to be freed from evil? Hear David, who says: "I said: I will confess against myself my injustice to the Lord, and you have forgiven the impiety of my sin." Praise God and be angry against sin, and do not defend sin, because to defend sin is a twofold sin.

Collationes de Septem Donis, Collation 3 ↗