No one returns from Christianity to the same state he was before Christianity but into a worse state: the difference between a pagan and an apostate is the difference between an unmarried woman and an adulteress. For faith perfects nature but faith lost corrupts nature. Therefore many men of our time have lost not only the supernatural light but also the natural light which pagans possessed.
The Latin Letters of C.S. Lewis (ed. St Augustine PressInc, 1988) - ISBN: 9781890318345