Full title runs like this: Letters to Malcolm, Chiefly on Prayer: Reflections on the Dialogue Between Man and God. Whew. Looks impressive or utterly geeky when you whip this one out on the bus, doesn't it? Or pretentious. At any rate, the book is marvellous and worth every snap judgement your fellow passengers may make, because it all comes down to the fact that C.S. Lewis was a smart guy, and it shows even in the a batch of letters that he never intended (to my knowledge) to publish.
I know I'm merely one of the tons of people who can claim that C.S. Lewis has been profoundly influential in the development of my faith, but it's very very true. I spent one whole summer with my friend Becca reading every Lewis book we could get our hands on, with the result that I catch myself constantly interjecting, in theological discussions, "Well, you know, in The Four Loves C.S. Lewis addresses that very topic. He says..." Makes me feel copy-cattish when I put it like that, but it's true. In a way, he has an answer for everything, even if the answer is sometimes "I don't know."
LETTERS TO MALCOLM is a skinny little over-looked book of letters, probably published after Lewis' death and therefore probably without his consent. There is no introduction to explain who Malcolm is, and Malcolm's response letters are not included--but it's just as well, because we get all we need from Lewis' side of the dialogue. I don't know why MALCOLM isn't more widely read; it ought to be. The chapters are short and concise, the topics big but well-written, and exciting to read. I will come back to this one, I can tell, just like I return constantly to Mere Christianity and L'Engle's Walking on Water.