Psalm 19 is an amazing Gospel tract broken into five parts. All five parts are necessary for salvation.
Page 1- An acknowledging of the Creator, God
Page 2- God's Word which confronts us about God's holiness and our sin
Page 3- Conviction of the Holy Spirit, where the Spirit takes the Word of God and shows us as sinners needing a Saviour
Psalm 19:12 "Who can understand his errors? cleanse thou me from secret faults. Keep back thy servant also from presumptuous sins; let them not have dominion over me: then shall I be upright, and I shall be innocent from the great transgression."
David not only acknowledges he is a sinner, but he rejects his sin. He turns from it! Repentance is a change of mind that produces a change in the direction we face. Whereas we were once turned toward sin, embracing it, and loving it, repentance is when sin becomes ugly, vile, and dirty in our eyes. That ugliness will cause a change in direction. When we were once turned toward sin, we then turn toward God instead. It is a humbling that causes us to seek God's forgiveness because He is holy and we are not. We realize we are the enemies of God yet no longer desire to be His enemy.
We call out to Him in repentance, "Cleanse me! Free me from the bondage of sin!"
David here admits that God must do the work. God must cleanse. God must break him free from the dominion of sin. We, too, must understand we cannot cleanse ourselves. We cannot break free. We will never be good enough or do enough good to earn salvation. Jesus paid for our sins, was buried, and rose again victorious so that we could have a way to be forgiven. He died in our place. We must repent, confess, and turn to Him.
Acts 3:19 "Repent ye therefore, and be converted, that your sins may be blotted out..."
For those of us who are saved, there is also a warning about sin. It has a progression if it isn't dealt with. David admits secret sin. Then he asks God to keep him back from presumptuous sin. That is sin that is proud, open, and arrogant. No shame. (There is a lot of that on social media. I have never been more shocked than when I see some of the things some professing Christians post about openly.) And then there is great transgression. There are some sins that go so far as to impact us for the rest of our lives. There are some sins that disqualify us from serving God in certain areas. There are some sins that mar our testimony so deeply that we are rendered ineffective for Christ. And there is a continuing in sin that God gives warning that we can cross the line... sin unto death. If we don't deal with secret sins, they will develop into presumptuous sins. And when we don't repent, they can turn into great transgression.
Revelation 3:19 "As many as I love, I rebuke and chasten: be zealous therefore, and repent."