"Cleanse" means "purge." But it is based on the word for sin (chattah) and literally means "de-sin” me. David wanted to have his sin completely purged away. He did not want to retain even a stain of it. "Wash” refers to the lustrations of the law. Centuries later Isaiah would write, "Though your sins are like scarlet, they shall be white as snow; though they are red as crimson, they shall be like wool" (Isa. 1:18). David wanted to be washed until he was as clean as that. "Blot out" refers to removing writing from a book, perhaps removing an indictment. It is the exact opposite of Pilate's words at the time of Jesus trial and crucifixion: "What I have written, I have written” (John 19:22).
Psalm 51 seems to be constructed on the basis of parallel statements in sets of threes. In part 1 we have already had three words that describe God as being merciful: mercy, love and compassion. We have had three words for sin: transgressions, iniquity and sin.
The second striking thing in these opening verses, which comes together with the first, is David's profound awareness of his sin and its true nature. In verse one he used three words to describe God's compassion. In verse two he uses three corresponding words to describe his sin.
David's sin, in which he committed adultery with Bathsheba and later, after discovering that she was pregnant, arranged to have her husband Uriah killed in battle, is the dark background for the psalm (see 2 Sam. 11, 12). But this very blackness led David to the light.
A person who does not have much experience studying the Bible is likely to think that a well-known passage must be easy to elaborate. "It must be easy to teach John 3:16, the twenty-third Psalm or the Christmas story,” he might say. Actually, the well-known passages are the hardest, and some seem almost impossible to expound.
