The Book People are people who preserve books for future societies by memorizing them.
When Montag first reads a book, he is impressed. Books seem much more real than the television that most people spend their time with. He seeks out Faber, an ex-English professor, and they plot to frame the firemen by planting books in their houses.
Faber is one of the book people. He and the rest of the group do not necessary all gather in one place together. They are spread out. Each one memorizes a book in order to protect it until the world is safe for books again.
Montag realizes this when he meets some of the book people after escaping. Since he attempted to memorize the Book of Ecclesiastes, he becomes the backup.
"Montag." Granger took Montag's shoulder firmly. "Walk carefully. Guard your health.
If anything should happen to Harris, you are the Book of Ecclesiastes. See how important you've become in the last minute!" (Part 3)
It is a brave new world for Montag. He is able to be a part of something that matters. When the city is destroyed in the bombings of the oft-ignored war, he and the other book people head there to pick up the pieces and try to rebuild civilization.
The Book People are people who memorize books so the firemen cannot harass them when they burn their books because they have memorized them. Granger is the head of the Book People.