Please help me explain the meaning of the following quote in Fahrenheit 451."What traitors books can be! You think they're backing you up, and they...

Beatty is suggesting that books are animate, personifying
them as beings with minds of their own and the ability to "turn" on readers. This
concept is used often in debates and can be supported when considering perceptions.
While I might read and interpret a book a certain way, you might disagree with my
interpretation. The same book could support both viewpoints, simply by the nature of
interpretation. Someone writing an essay in favor of the death penalty, for instance,
might use the same text as a person who writes an essay to oppose it; Beatty is
essentially bemoaning this possibility, with the addition of his opinion that a person
can become "lost" in the words--the nouns, verbs, and adjectives--that comprise the
text. Beatty's perception of books here is how he justifies the burning of them. They
are, to him, two-faced and essentially evil, and therefore deserve to be burned. This
affects Montag in his process of thought, a major theme, which is how he changes
throughout the book--his thinking is altered based on his initial meeting with Clarisse,
and by the time Beatty reaches him, Montag is finished with book
burning.