If Christianity is true then it ought to follow (a) That any Christian will be nicer than the same person would be if he were not a Christian. (b) That any man who becomes a Christian will be nicer than he was before. Just in the same way, if the advertisements of Whitesmile’s toothpaste are true it ought to follow (a) That anyone who uses it will have better teeth than the same person would have if he did not use it. (b) That if anyone begins to use it his teeth will improve…. Christian [Jane]* Bates may have an unkinder tongue than unbelieving Dick Firkin. That, by itself, does not tell us whether Christianity works. The question is what Jane’s tongue would be like if she were not a Christian and what Dick’s would be like if he became one. Jane and Dick, as a result of natural causes and early upbringing, have certain temperaments: Christianity professes to put both temperaments under new management if they will allow it to do so. What you have a right to ask is whether that management, if allowed to take over, improves the concern. Everyone knows that what is being managed in Dick Firkin’s case is much ‘nicer’ than what is being managed in Jane Bates’s. That is not the point. To judge the management of a factory, you must consider not only the output but the plant. Considering the plant at Factory A it may be a wonder that it turns out anything at all; considering the first-class outfit at Factory B its output, though high, may be a great deal lower than it ought to be. No doubt the good manager at Factory A is going to put in new machinery as soon as he can, but that takes time. in the meantime low output does not prove that he is a failure.
*Lewis wrote about the fictional characters “Miss Bates” and “Dick Firkin.” It’s a bit clunky in modern English, and since they are only fictional characters, I’ve decided to represent the names equally: Jane Bates and Dick Firkin, or Jane and Dick; no more Miss Bates and Dick.
C.S. Lewis, Mere Christianity (1952; Harper Collins: 2001) 208-209.