Psalm of penitence and restoration. The psalm follows David's adultery with Bathsheba, and precedes Ps 32.

v1-2: Forgiveness is based on God's mercy and faithfulness, "according to your..." Since his sins were great, David asked, blot out / wash me thoroughly / cleanse me; he was confident that God would do this. David described his sins as; transgressions, iniquity, sin; for he recognised his guilt before God, and offered no excuses for his sins.

We recall that David's repentance was not immediate.

v3-4: Our response is deep repentance. All sin is firstly against God (Gen 39.9); and repentance acknowledges our sin and guilt, and His righteousness. Only God is totally just and righteous, and therefore only He has the authority to judge sins; further, since He is merciful, we can come before Him with repentance.

v5-6: Since our motives are not good, for we were even conceived in sin, we need to be saturated in the truths of God; we need truth in the inner parts, in our heart and emotions, our mind and attitudes, our will and decisions; all is to be directed by His words. This is not just innocence, but integrity and righteousness.

v7-9: The Lord will cleanse, for He alone knows the depths of our sins. Only if He washes me shall I be clean, even whiter than snow.

There is a hint here at the suffering David had endured prior to his repentance, for his bones were "crushed"; this describes his sorrow of heart, his uneasy conscious. If we fail to repent, or if we cherish sin in our heart, it will do us no good.

v10-12: Confession and forgiveness are followed by restoration, joy and gladness (v8). Again, unless the Lord restore, our guilt remains. A clean heart is from God, Deut 30.6. David feared estrangement from God, and asked God to do a full and deep work in Him.

The power of sin is reflected in; '‘A transgression, a crime, entering a man’s existence, eats it up like a malignant growth, consumes it like a fever.’ (Joseph Conrad, Nostromo, page 429).

v13: Once restored, we can testify, that others might turn to God.

v14: "Blood-guiltiness", causing others to sin. Avoid being responsible for the sins of others, Matt 18.6. Rather, proclaim God's righteousness by living a life of blamelessness.

v15: The restored man can also sing praises to God once again.

v16-17: Animal sacrifices are useless without a right heart (Mic 6.7-8; 1 Sam 15.22; Ps 50.7-15; Heb 9.13-14); indeed, there was no sacrifice for adultery and murder anyway. David could only bring a broken and contrite heart, the "righteous sacrifices."

Jonathan Edwards makes the comment that a tender heart is achieved by godly sorrow, rather than by legalism and criticism (two long quotes here):

‘gracious affections are of a quite contrary tendency; they turn a heart of stone more and more into a heart of flesh. A holy love and hope are principles that are vastly more efficacious upon the heart, to make it tender, and to fill it with a dread of sin, or whatever might displease and offend God, and to engage it to watchfulness, and care, and strictness, than a slavish fear of hell.’

‘Gracious affection, as was observed before, flow out of a contrite heart, or (as the words signifies) a bruised heart, bruised and broken with godly sorrow; which makes the heart tender, as bruised flesh is tender, and easily hurt. Godly sorrow has much greater influence to make the heart tender, than mere legal sorrow from selfish principles.’ (Jonathan Edwards, Religious Affections)

v18-19: God's people to share in the blessings of restoration; the references here are to regular sacrifices of worship to God.