At first glance, P. D. James's novel The Children of Men and the movie The Book of Eli don't appear to have all that much in common, but when we look more closely, we see several similarities.
Both works take place in a world gone mad. In the movie, nuclear war has happened, and destruction abounds. Much has been lost, and Eli has a mission to carry the one remaining copy of the Bible to safety. In the novel, there has not been war, but human destruction is imminent, for no children have been born in England for many years. Theo ends up with the mission of keeping the pregnant Julian and the first new child safe.
The theme of religious faith stands at the heart of both works. A voice in Eli's head in the movie leads him to the copy of the Bible, and he firmly believes that he will be safe during his journey. Julian and the other members of the Five Fishes in the novel are also guided and encouraged by their faith.
For much of the rest of the world in both works, faith no longer plays any role. Power is key instead. Carnegie in the movie takes full advantage of his power. He does not care whom he hurts as long as he remains in control. Xan in the novel feels much the same way. They both rule supreme and do not tolerate dissidents.