In Fahrenheit 451, Granger tells Montag that the Book People are "...all bits and pieces of history and literature and international law..." They have saved the written words of important authors in their memories. Granger tells Montag that it is better to "keep it in the old heads, where no one can see it or suspect it." After the war, Granger feels that their collective knowledge may help civilization rebuild itself.
Many of the authors mentioned were revolutionary in their time: Paine wrote The Age Of Reason, The Rights Of Man and Common Sense, the latter published during the American Revolution. Machiavelli's famous work The Prince established his place as the preeminent father of political theory. Buddha's name itself means "the enlightened one" or "the awakened." All these authors stressed independence of thought, the rights of the individual, and the importance of self-reflection. You will notice that throughout Bradbury's novel, characters like Millie are hypnotized into a state of near catatonic stupor through daily inundation of senseless programming from wall-length televisions. These characters have lost the self-discipline of concentrated thought. Montag tells Granger that he can't remember anything about Millie. His anguished confession is heartbreaking:
"I think of her hands but I don't see them doing anything at all. They just hang there at her sides or they lie there on her lap or there's a cigarette in them, but that's all."
Bradbury's novel is prescient (having foresight): pervasive technology has rendered our collective thoughts impotent and caused us to forget all the great ideas of philosophy and history that have made advanced civilization the epitome of progress. Freedom of thought and independence of judgment have been sacrificed at the altar of fairness. The Book People want to preserve what has been censored, and no government, no matter how draconian, can ever extricate what has been carefully saved in the hearts and minds of free individuals. This is the implication of the hobos' words.
You may be interested in Bradbury's own words from an article by his authorized biographer, Sam Weller:
Fahrenheit 451, Bradbury said, was a depiction of a society willfully dumbing itself down by staring at screens, stuffing its collective consciousness with useless factoids, empty ideas and throwaway reality.
Thanks for the question.