"I says to myself, ‘What’s gnawin’ you? Is it the screwin’?’ An’ I says, ‘No, it’s the sin.’ An’ I says, ‘Why is it that when a fella ought to be just about mule-ass proof against sin, an’ full up of Jesus, why is it that’s the time a fella gets fingerin’ his pants buttons?’"
– John Steinbeck
The Grapes of Wrath, Chapter 4. Jim Casy’s spiritual journey has led him to question if having sex with girls while a practising religious minister is really a sin, or just something natural. Being "full up of Jesus" should be proof against sin, he feels.