In Part Three of Fahrenheit 451, Montag is walking along the railroad tracks when he meets with a group of former college professors. The head of their group is Granger, who enthusiastically welcomes Montag to join them.
These professors are social outcasts, driven from the city for book-related crimes. Granger, for example, has been on the run since he struck a fireman who had discovered his secret (and illegal) library and tried to burn it.
These men have an important conversation about the future. When the time comes, these men plan on rebuilding society so that literature is no longer illegal or forgotten. To do this, each man has memorized a book so that the great works of literature will not be lost. When the time comes, each man will recite the words so that they can be written down for future generations. During their conversation, Montag agrees to memorize the Book of Ecclesiastes, a sign of his commitment to staying with this group of men and to creating a future without censorship.
Montag's walk along the railroad tracks is the classic symbolic quest and he is rewarded at the end when he meets a group of learned men--mostly professors-- who have remained on the fringes of society because they are the keepers of books. Remarkably, thes men "keep" books in their memories and each man has memorized a book or two that they believe to be valuable or essential to the human race. These men believe it is their responsibility to hold what small bits of the past they can so that, perhaps, at some point in the future, when books and men like themselves are valued, they will prepared and ready to help rebuild.
He meets a group of men who have previously fled from the city or from other cities and have been working to try and create a "library." Granger, their leader, tells Montag about what they've done and how they've decided that they have to actually memorize portions of or entire books and just to keep them in their heads and perhaps someday be able to put them down on paper again. The men are often referred to as the books they've memorized. And they speak of others in other places that have memorized other books.
Montag tells them that he feels bad but he only remembers a portion of the bible.