Why did Bradbury use Alexander Pope in Fahrenheit 451?
In this section of Part II, Montag has returned to the firehouse after talking with Faber. Beatty and the other firemen are playing cards. Beatty uses this as an opportunity to make the case (to Montag) that he's read a good amount but that, in the end, books only lead to destruction. Beatty is an unwitting hypocrite because he uses knowledge from books to make the point that such knowledge is dangerous (even though he's using that knowledge for his own "useful" purposes).
In discussing certain authors and making certain quotes, Beatty handpicks phrases and maxims out of context to make his points. He quotes from Alexander Pope's "An Essay on Criticism" which is a work on literary criticism. "An Essay on Criticism" is therefore, a text that instructs the critic how to judge literature, how to judge books. But whereas Pope was trying to instruct the critic to recognize and celebrate great literature, Beatty was using Pope's words out of context to judge and denounce literature.
That's why Beatty uses these quotes. Out of context, they suit his purposes:
Words are like leaves and where they most abound, Much fruit of sense beneath is rarely found.
Beatty twists this quote to imply that too many words and too many pages (leaves) yield no real sense or truth. But Pope was actually making the point to be precise (rather than verbose) when writing.
A little learning is a dangerous thing. Drink deep, or taste not the Pierian spring; There shallow draughts intoxicate the brain, and drinking largely sobers us again.
Here, Beatty tries to make the point that drinking (absorbing) a little knowledge from books will make you less logical and irrational - drunk. However, Pope was indicating that one should not just read and learn a little. Quite simply, it is better to learn profound truths rather than cursory knowledge of tiny bits of information. Pope also meant that learning just a little bit can be misleading. Beatty uses this quote to say that knowledge from books is dangerous (intoxicating). That's why he calls Montag a "drunkard."