However, he also realized that as an imperfect man he needed the aid of his Maker in conducting himself aright. This is clear from the concluding portion of Psalm 19. We read: “Mistakes​—who can discern? From concealed sins pronounce me innocent.

Ps. 19:12-14.

David realized that as an imperfect man he might commit sins of which he was not even aware. So he asked to be forgiven the transgressions that might have been hidden from him.