Mere Christianity, in The Complete C. S. Lewis Signature Classics

p. 55

“Some of us who seem quite nice people may, in fact, have made so little use of a good heredity and a good upbringing that we are really worse than those we regard as fiends.  Can we be quite certain how we should have behaved if we had been saddled with then psychological outfit, and then with the bad upbringing, and then with the power, say, of Himmler?  That is why Christians are told not to judge.  We see only the results which a person’s choices make out of his raw material.  But God does not judge him on the raw material at all, but on what he has done with it.”