I reread Frank Herbert's Dune recently. Things are so much clearer once you know more about Islam and the Qu'ran and some of the rituals there as well as Zen Buddhism and other topics such as Christianity and the Kaballah.
Magnificent book to be honest, he manages to drag you into the story and totally washes over you with a imaginary, yet possible future of mankind.
Dune Messiah is a most bizarre follow-up tale. Hard to describe what you read in those meager 200 pages, but they nonetheless make a tremendous impact. Amazing, just amazing.
The Butlerian Jihad was quite an interesting read by Brian Herbert, Frank's son, to learn about the events that lead to the extermination of the thinking machines, the rise of the sorceresses, the Tleilaxu, Zensunnis and Zenshi'ites.