The men Montag meets at the end of the novel are personifications of famous books or parts of books. Granger tells him that we all have photographic memories, but we have lost the ability to recall things during our lifetime. They have found a method where,
"....we can recall anything that's been read once." (pg 151)
Each man represents a book. However, if that man dies, so does his knowledge. When Granger asks Montag what he has to offer, Montag tells him,
"Nothing. I thought I had part of the Book of Ecclesiastes and maybe a little of Revelation,but I haven't even that now. (pg 150)
Granger assures him that it will come back to him. They have one other person who has read the Book of Ecclesiastes, but Granger warns Montag,
"Guard your health. I anything should happen to Harris, you are the Book of Ecclesiastes. See how important you've become in the last minute!" (pg 151)
Granger explains how they got together and the philosophy behind the books.
"We read the books and burnt them, afraid they'd be found. Microfilming didn't pay off; we were always traveling; we didn't want to bury the film and come back later. Always a chance of discovery. Better to keep it in the old heads, where no one can see it or suspect it. We are all bits and pieces of history and literature and international law." (pg 152)
There are thousands of these people on the road. They plan to pass the knowledge onto their children. Some of it will be lost in the process but they hope that some time in the future, they will be able to bring back the knowledge.
If referring to the links below, look up "Granger" under characters.