I know this review is quite late but I just wanna share my insights about the movie.
The Book of Eli revolves around the importance of a book which the surviving inhabitants of Earth after a great tragedy is fighting for. In the future times where rights and respect are forgone and the land has been desolate that food and water is the most important thing, the book is seen as a weapon of control. The book that is the center of the movie is the Holy Bible. Religion is seen as a weapon of getting people with no hope to hope in the person who possess the Bible.