Albert Barnes Commentary Psalms 51:4

"Against thee, thee only, have I sinned, And done that which is evil in thy sight; That thou mayest be justified when thou speakest, And be clear when thou judgest." — Psalms 51:4 (ASV)

Against you, you only, have I sinned - That is, the sin, considered as an offense against God, now appeared to him so enormous and so aggravated, that, for the moment, he lost sight of it considered in any other of its bearings. It was a sin, as all other sins are, primarily and mainly against God; it derived its chief enormity from that fact.

We are not to suppose that David did not believe and notice that he had done wrong to people, or that he had offended against human laws, and against the well-being of society. His crime against Uriah and his family was of the deepest and most aggravated character, but still the offense derived its chief heinousness from the fact that it was a violation of the law of God. The state of mind here illustrated is that which occurs in every case of true penitence.

It is not merely because what has been done is a violation of human law; it is not that it brings us to poverty or disgrace; it is not that it exposes us to punishment on earth from a parent, a teacher, or civil ruler; it is not that it exposes us to punishment in the world to come: it is that it is of itself, and apart from all other relations and consequences, an offense against God; a violation of His pure and holy law; a wrong done against Him, and in His sight.

Unless there is this feeling, there can be no true penitence. And unless there is this feeling, there can be no hope of pardon, for God forgives offenses only as committed against Himself—not as involving us in dangerous consequences or as committed against our fellow men.

And done this evil in your sight - Or, when Your eye was fixed on me. (Compare the notes at Isaiah 65:3). God saw what he had done; and David knew, or might have known, that the eye of God was upon him in his wickedness.

It was to him then a great aggravation of his sin that he had dared to commit it when he knew that God saw everything. The presence of a child—or even of someone with very limited understanding—would restrain people from many acts of sin which they would venture to commit if alone; how much more should the fact that God is always present, and always sees all that is done, restrain us from open and from secret transgression.

That you might be justified when you speak - That Your character might be vindicated in all that You have said; in the law which You have revealed; in the condemnation of the sin in that law; and in the punishment which You may appoint.

That is, he acknowledged his guilt. He did not seek to apologize for it, or to vindicate it. God was right, and he was wrong.

The sin deserved all that God in His law had declared it to deserve; it deserved all that God by any sentence which He might pass upon him would declare it to deserve. The sin was so aggravated that any sentence which God might pronounce would not be beyond what it justly deserved.

And be clear when you judge - Be regarded as right, holy, pure, in the judgment which You may appoint. (See this more fully explained in the notes at Romans 3:4).