Psalms 51:3

For I acknowledge my transgressions - literally, I know, or make known. That is, he knew that he was a sinner, and he did not seek to cloak or conceal that fact. He came with the knowledge of it himself; he was willing to make acknowledgment of it before God. There was no attempt to conceal it; to excuse it. Compare the notes at Psalms 32:5. The word ““for”” does not imply that he referred to his willingness to confess his sins as an act of merit, but it indicates a state of mind which was necessary to forgiveness, and without which he could not hope for pardon.

And my sin is ever before me - That is, It is now constantly before my mind. It had not been so until Nathan brought it vividly to his recollection (2 Samuel 12:1 ff); but after that it was continually in his view. He could not turn his mind from it. The memory of his guilt followed him; it pressed upon him; it haunted him. It was no wonder that this was so. The only ground of wonder in the case is that it did not occur “before” Nathan made that solemn appeal to him, or that he could have been for a moment insensible to the greatness of his crime. The whole transaction, however, shows that people “may” be guilty of enormous sins, and have for a long time no sense of their criminality; but that “when” the consciousness of guilt is made to come home to the soul, nothing will calm it down. Everything reminds the soul of it; and nothing will drive away its recollection. In such a state the sinner has no refuge - no hope of permanent peace - but in the mercy of God.