The BBC asked C.S. Lewis during World War II to do some radio programs about the fundamentals of Christianity.  He started these 15 minutes broadcasts in 1941, and they came together in part as the book  "Mere Christianity,” published in 1952. It is a timeless classic as influential today as when Lewis originally wrote it.

The book takes us from when Lewis was an Atheist through his ultimate conversion to Christianity. The book looks closely at what it calls moral law and says that understanding it is essential. His sense of humanity's failure to keep the moral law is key to how he sees Christ's work in overcoming the effect of Satan's rebellion.

It gives a comparison to other views of what God is. He states that Christ either was God or was not or just thought he was, and then based on Christ's character, he concludes that he was. The book looks at how Christian beliefs result in creditable ethics.  

An introductory look at Christianity serves as a fundamental touchstone for Christian discourse.