In C.S. Lewis's quote, I believe he means that books only add to our life. Some people may think that literature only describes the things we already know, but it actually gives us more than what we have. Books add to the skills we need to live out our lives. They enhance our imagination, and sometimes even our ways of handling certain situations. The quote also describes how our lives may be boring and mechanical, but books can add more fun and excitement to them.
The book that I read, "Rebecca," relates to this quote because of the ways it changed my point of views on things. It also added much more excitement, to the point that it made my head hurt. "Rebecca" is an extremely good book most likely one of the best ones I've read, even though it made me verrrrry angry.