For I know my transgressions, and my sin is ever before me. Against you, you only, have I sinned and done what is evil in your sight, so that you may be justified in your words and blameless in your judgment. Behold, I was brought forth in iniquity, and in sin did my mother conceive me. – (Psalm 51:3-5 ESV)
“We are often like Adam. He sinned along with his wife in eating of the fruit of the tree of the knowledge of good and evil. But when God came to him in the garden demanding, “Have you eaten from the tree that I commanded you not to eat from?” (Gen. 3:11), Adam did not confess his transgression. Instead he began to shift the blame to other people and eventually to God himself. He said, “The woman you put here with me—she gave me some fruit from the tree, and I ate it” (v. 12).
It was the same with Cain. Cain killed his brother. But when God came demanding, “Where is your brother Abel?” Cain answered, “I don’t know. Am I my brother’s keeper?” (Gen. 4:9).
And what about Abraham? Abraham lied about his wife, Sarah, saying she was his sister, because he feared that the men of the Negev would kill him for her. When he was found out he excused himself, saying that it was not an outright lie: “Besides, she really is my sister, the daughter of my father though not of my mother; and she became my wife” (Gen. 20:12).
This is not how David prayed. David acknowledged his sin, laying it out and confessing it utterly. This is the significance of verse 4: “Against you, you only, have I sinned.” Many commentators have pointed out that this was not strictly true. David had sinned against Bathsheba and against Uriah, her husband. He sinned against the armies of Israel, who lost their battles during the time of David’s sin. He sinned against the nation. But in the sight of the perfection and majesty of God, David knew that these wrongs fell into relative insignificance. The greatest of all problems with sin is that it is an offense against God. It would make a vast difference in many lives if people could only see this. David did see it. Therefore, he did not try to cover sin up, but confessed it, saying, “Against you, you only, have I sinned.”
Another aspect of David’s confession is his acknowledgment that it is not only that he sinned once, but that his whole nature was permeated with sin: “Surely I was sinful at birth, sinful from the time my mother conceived me” (v. 5). This verse says nothing about sex being wrong. This is the way it has been interpreted in some sectors of the Roman Catholic Church as the result of an asceticism that became a goal of Catholic piety during the early and late Middle Ages. But this is not what David is talking about. He is saying that there was never a moment in his life when he was free from sin and no part of his being escaped sin’s contamination. It is the same with us. By ourselves we have never done anything to please God; everything we have done is contaminated by sin. But God can cleanse us. He can begin a work that will enable us to live victoriously.”
While I regarded God as a tyrant, I thought sin a trifle; but when I knew him to be my father, then I mourned that I could ever have kicked against him. When I thought that God was hard, I found it easy to sin; but when I found God so kind, so good, so overflowing with compassion, I smote upon my breast to think that I could ever have rebelled against one who loved me so, and sought my good. – Charles Spurgeon
Boice, J. M. (1998). Genesis: An expositional commentary (928–929). Grand Rapids, MI: Baker Books.