"If conversion to Christianity makes no improvement in a man’s outward actions—if he continues to be just as snobbish or spiteful or envious or ambitious as he was before—then I think we must suspect that his “conversion” was largely imaginary; and after one’s original conversion, every time one thinks one has made an advance, that is the test to apply. Fine feelings, new insights, greater interest in “religion” mean nothing unless they make our actual behavior better; just as in illness “feeling better” is not much good if the thermometer shows that your temperature is still going up."

C.S. Lewis, Mere Christianity, p. 207