When a man turns to Christ and seems to be getting on pretty well (in the sense that some of his bad habits are now corrected), he often feels that it would now be natural if things went fairly smoothly. When troubles come along-illnesses, money troubles, new kinds of temptation-he is disappointed. These things, he feels, might have been necessary to rouse him and make him repent in his bad old days; but why now? Because God is forcing him on, or up, to a higher level: putting him into situations where he will have to be very much braver, or more patient, or more loving, than he ever dreamed of being before. It seems to us all unnecessary: but that is because we have not yet had the slightest notion of the tremendous thing He means to make of us.
--C.S. Lewis, Mere Christianity
