"Mere Christianity" by CS Lewis is perhaps one of the most profound books on the topic of religion that I have ever read.
While I disagree with Lewis on matters of denomination and ordinance, for a theology, "Mere Christianity" leaves one quite fulfilled if not curious about the life of Christ.
Lewis takes his literary and academic approach to the matter of whether or not Christ really was who He said He was and who His disciples said he was. He compares and contrasts Christianity, or the need for a Messiah with other religions of our day and of the past and goes on to demonstrate the need for a Redeemer, regardless of religious belief, and demonstrates quite successfully (I thought anyways) that any notion of "it doesn't really matter what you believe" to be quite absurd in terms of how the universe operates and what it is truly founded upon.
In other words, when we read about the Life of Christ, anyone who thinks he was merely a good man or a prophet has completely missed the essence of the stories of the life of Christ, and Lewis does an excellent job demonstrating this. Even those who believe He truly was the Messiah will come away with a deeper appreciation for the necessity of an atonement in this world and the notion that the world simply could not exist without such an atonement.
A thought provoking, deep and yet easy read, "Mere Christianity" is probably one of the top ten books I've ever read. I would recommend it to anyone who truly wants to understand Christianity as a whole as to what it's purpose and vision is, or who wants to read how an Atheist and a Doctor of Literature came to believe not only in the Messiah but in the need and purpose of a Messiah and his thoughts on the subject.
Nobody writes better than Lewis, I believe, and "Mere Christianity" has to be one of the most influential Christian apologetic works of the 20th century, I highly recommend it!