Psalms 51:2

Psalms 51:2. Wash me thoroughly from mine iniquity,

The forgiveness of sin is not enough for the true penitent; he wants the defilement, which he has incurred through sin, also to be removed. If washing will not suffice, he asks the Lord to try any other method that will accomplish the desired end.

Psalms 51:2. And cleanse me from my sin.

"If fire is needed to purify me, use fire, O Lord, only ‘cleanse me from my sin.’