I’m a big Lewis fan; I credit him and a few other influences with firming up my resolve to join the Catholic Church ten years ago, though Lewis himself was Anglican. I’ve read all his books, and I’m actually thinking your friend might benefit from following up Mere Christianity with one of Lewis’ fiction works. I’d recommend The Great Divorce, which is based on an old theological theory called the Refrigerium: the idea is that every so often, the damned souls in Hell are allowed a sort of ‘day-trip’ to Heaven to see if they might want to stay. If so, they must surrender their sinful selves to Christ’s transforming love; if not, they are perfectly free to return to Hell. Lewis’ book is a portrayal of one of these day-trips, and he uses the fanciful premise to make excellent points about free will, the fact(or not) of pre-destination, and the theological necessity for the idea of eternal damnation. It’s a great read, and not at all long. Of course, the Chronicles of Narnia are an obvious recommendation; all the adult friends, religious or not, to whom I have recommended them have raved about how wonderful they were. The Screwtape Letters is also good, but if I were your friend I’d read The Great Divorce first; it’s slightly more serious than Screwtape, and may help to answer some questions he might be having.
