What does Psalm 51:1 mean?
In many of David's psalms he addresses God as "my God," but his sin had removed him from close fellowship with God, so in this verse he prays, "O God." David knew God well enough to know Him as gracious, loving, and merciful. And so, he cries out to God to show unfailing love and abundant mercy by blotting out his transgressions. Transgressions indicate a revolt against God. By violating God's commandments against adultery and murder, David had rebelled against God, and he knew only God's grace, love, and abundant mercy could erase his sin.In Old Testament times, when crimes and debts were forgiven or paid, they were blotted out—erased—from the book in which they were written. When God forgives sin, He similarly blots it out. The apostle Peter urged a crowd that had gathered in Solomon's Portico to repent "that your sins may be blotted out" (Acts 3:19). Micah 7:19 assures us that our pardoning God casts all our sins into the depths of the sea.
Psalm 51:1–7 is David's plea for mercy and cleansing. He admits he has sinned against God. His approach to confession is to take God's attitude toward sin. He sees his sins as transgressions, iniquity, evil, and the result of his lifelong offensive nature. First John 1:9–10 corresponds to this passage by teaching believers to confess their sins—to agree with God's stance about those sins—with the promise of God's forgiveness and cleansing.
This psalm opens with David's plea to God to show him mercy. He asks God to blot out his transgressions, wash his iniquities, and cleanse him from sin. He admits his sinning was against God. He also confesses his human sin nature. David asks God to make him as white as snow by purging him with hyssop. He longs for joy to return to him, but knows he was suffering because God had turned away from him. He pleads with God for a clean heart and a right spirit. He does not want God to cast him aside and remove His Holy Spirit. David longs for a renewal of the joy of his salvation. If cleansing from sin occurred and joy returned to him, David would teach transgressors God's ways, and sinners would be converted. He promises near the end of the psalm to declare God's praise if God would forgive him. He knew it would be futile to offer a sacrifice to God, because God delights in a broken and contrite heart and not in sacrifices offered with an unrepentant heart. David closes the psalm with a prayer for God to bless Jerusalem.