C. S. Lewis (1898-1963) was not a preacher or theologian, but his writing on Christianity are still read by millions. His Chronicles of Narnia is still popular with children (and adults) worldwide. He was a professor of English literature and an atheist for some time. Once he was converted to Christianity, he wrote extensively about his faith.
I've read some of his books like Mere Christianity or Screwtape Letters, but I found it hard to absorb what he was trying to say. I found that I could better understand him by reading short portions at a time rather than reading straight through a book.
That's why I love A Year with C. S. Lewis: Daily Readings from His Classic Works, edited by Patricia S. Klein. Each day's selection contains an excerpt from one of his "signature classics." Why bite off more than you can chew when you can just have a little taste and go back for more when you're ready?
I took a year to read through my copy, and I've given it as a gift to others. It makes a good Christmas gift. There's an index at the end listing sources by book and by day so that you will be able to find each selection in the original book if you should want to read further on that topic.