The devil approached Martin Luther one day and said to him every person is fallible. He presented the Reformer with a long list of sins of which he was guilty. When he had finished reading, Luther said to Satan, “Think a little harder; you must have forgotten some.” This the devil did and added other sins to the list. At the conclusion of this exchange, Martin Luther simply said, “That’s fine .’ Now write across that list in red ink, ‘The blood of Jesus Christ, His Son, cleanses us from all sin.” The devil walked away in silence.
Baker Books, 1500 Illustrations for Biblical Preaching, by Michael P. Green