Read Psalm 51

Purify me from my sins, and I will be clean;
wash me, and I will be whiter than snow.
Oh, give me back my joy again;
you have broken me—
now let me rejoice.
Don’t keep looking at my sins.
Remove the stain of my guilt.
Create in me a clean heart, O God.
Renew a loyal spirit within me.
Do not banish me from your presence,
and don’t take your Holy Spirit from me.
Psalm 51:7-11 (NLT)

Psalm 51, which David wrote after being confronted about his sin with Bathsheba, is one of the most famous psalms.
Our disobedience separates us from God, and takes away the joy that comes from being in the will of God. And even after we are forgiven, there are still consequences to our sin that continue to play out in our lives. So it’s an act of faith to believe that it’s done—that once I’ve confessed my sin and come to God with a humble and contrite heart, he truly does forgive me.