This psalm is written in the context of the terrible sin David committed against the Lord in his adultery with Bathsheba. He compounded the sin by arranging for Bathsheba’s husband Uriah to be put up front on the battlefield so his death would be assured. It seems David went for some time without thinking of the grievous nature of the murder and adultery he had committed.

The Lord sends Nathan the prophet to confront David, and expose his sin to him. The Holy Spirit cuts through David’s soul in such a way he confesses: “I have sinned.” In the psalm David considers the greatness of the weight of sin as well as the greatness of the weight of forgiveness and cleansing from sin.

Nobody seeks grace who doesn’t know of the weight of sin. We shouldn’t think because we haven’t committed as grievous sin as David did that we don’t have the same sinful nature or the same need of forgiveness and cleansing. If we are not as sinful in acts as our neighbor we are nevertheless likewise sinners.

Therefore it behooves us to consider the sinfulness of sin within us. David uses several terms to define sin (verses 1-3). The word for “transgression” carries the disposition of rebellion, resistance and revolt toward rightful authority. The ultimate authority is God. David’s rebellion was against God.

The word for “iniquity” means twistedness in the heart. The sinful acts (or thoughts) spring from the twisted nature or depravity within. David recognizes this and he pleads with the Lord to do an operation that will effectively cleanse his heart. The last term he uses, translated “sin,” has the common meaning of missing the mark, as an archer would miss his target. Paul describes it as all have fallen short of the glory of God.

This is all bad news. Understand that David isn’t simply depressed and overstating his guilt. This is the Spirit of God instructing not just David but all who read it of how deep our need is of God’s grace. When David says he was born in iniquity (verse 5) he isn’t blaming his parents for his sin. He is acknowledging the reality of a depraved nature in himself and all men.

There are only two paths from this truth. You can deny it, and go your own way. Or you can seek a cure only God can provide. The good news from God is really good news. David’s desire is his sin be blotted out (verses 1 and 9). This term often referred to a tablet of wax with accounts payable on it wiped clean, forever gone. You can see what David means here.

David doesn’t want something erased as we would erase something written with a pencil that was offensive. He is thinking about the place of ultimate record keeping where things are indelibly written. He has in mind God’s book. We can’t erase what is in God’s book. It has recorded every thought and deed. There is someone who knows all. No one can excuse themselves.

God however, offers to blot out all our sin. No more record of it. He offers it in an incredible way. The Son of God atones for it. He dies under the just condemnation of it. His death is sufficient by God’s standard for whoever avails himself of him. David has in mind a sacrifice for his sins. He says, “Purge me with hyssop, and I shall be clean.”

Hyssop was a bushy plant with a lot of branches and leaves. It was used in sacrifices by dipping it into the blood of the sacrifice and shaking or sprinkling the blood all over as a sign of atonement for sin. All the Old Testament sacrifices pointed to the Lamb of God, the Lord Jesus Christ, who came to take away sin. David responds to such grace in the second half of the psalm.

If you know your sin, and know the shame and guilt of the record of it, then you can understand why the sinful woman washed Jesus feet with her tears, and why David speaks of the joy of salvation (verse 12) and praise to the Lord (verse 15). No more will superficial worship be sufficient for David (verse 16). David sees a right response to God’s grace as humble, thankful devotion (17) and offering up himself body and soul to the Lord (verse 19). Bulls (verse 19) were the most costly offering in David’s time. Paul speaks of the Christian, in response to such grace, offering themselves as living sacrifices.