Psalms 51:3

For I acknowledge my transgressions
Before God and man. Acknowledgment of sin is what the Lord requires, and promises forgiveness upon, and therefore is used here as a plea for it; and moreover the psalmist had done so before, and had succeeded in this way, which must encourage him to take the same course again; see ( Psalms 32:5 ) ;

and my sin [is] ever before me;
staring him in the face; gnawing upon his conscience, and filling him with remorse and distress; so that his life was a burden to him: for though God had put away sin out of his own sight, so that he would not condemn him for it, and he should not die; notwithstanding as yet it was not caused to pass from David, or the guilt of it removed from his conscience.