Charles H. Spurgeon on Psalms 51:9

Hide thy face from my sins. Do not look at them; be at pains not to see them. They thrust themselves in the way; but, Lord, refuse to behold them, lest if thou consider them, thine anger burn, and I die. Blot out all mine iniquities. He repeats the prayer of the first verse with the enlargement of it by the word "all." All repetitions are not "vain repetitions." Souls in agony have no space to find variety of language: pain has to content itself with monotones. David's face was ashamed with looking on his sin, and no diverting thoughts could remove it from his memory; but he prays the Lord to do with his sin what he himself cannot. If God hide not his face from our sin, he must hide it forever from us; and if he blot not out our sins, he must blot our names out of his book of life.