Charles H. Spurgeon on Psalms 51:2

Wash me throughly. It is not enough to blot out the sin; his person is defiled, and he fain would be purified. He would have God himself cleanse him, for none but he could do it effectually. The washing must be thorough, it must be repeated, therefore he cries, "Multiply to wash me." The dye is in itself immovable, and I, the sinner, have lain long in it, till the crimson is ingrained; but, Lord, wash, and wash, and wash again, till the last stain is gone, and not a trace of my defilement is left. The hypocrite is content if his garments be washed, but the true suppliant cries, "wash me." The careless soul is content with a nominal cleansing, but the truly awakened conscience desires a real and practical washing, and that of a most complete and efficient kind. Wash me throughly from mine iniquity. It is viewed as one great pollution, polluting the entire nature, and as all his own; as if nothing were so much his own as his sin. The one sin against Bathsheba, served to show the psalmist the whole mountain of his iniquity, of which that foul deed was but one falling stone. He desires to be rid of the whole mass of his filthiness, which though once so little observed, had then become a hideous and haunting terror to his mind. And cleanse me from my sin. This is a more general expression; as if the psalmist said, "Lord, if washing will not do, try some other process; if water avails not, let fire, let anything be tried, so that I may but be purified. Rid me of my sin by some means, by any means, by every means, only do purify me completely, and leave no guilt upon my soul." It is not the punishment he cries out against, but the sin. Many a murderer is more alarmed at the gallows than at the murder which brought him to it. The thief loves the plunder, though he fears the prison. Not so David: he is sick of sin as sin; his loudest outcries are against the evil of his transgression, and not against the painful consequences of it. When we deal seriously with our sin, God will deal gently with us. When we hate what the Lord hates, he will soon make an end of it, to our joy and peace.