Beatty gives Montag what their society was so good at witholding: information, things to think about, and the truth of how they got there. He gives Montag an entire history of their society, and of his profession. This outlines why books are banned, how they all lost the ability to think, and how that-in Beatty's opinion-is better. All of this information really answers a lot of questions that Montag has, and instead of resolving Montag's issues, the information just makes him more discontended. He doesn't want things to be the way that Beatty described; disillusioned, he leaves home and seeks out Faber, who is more of a like mind. Beatty also gives indirect permission for Montag to keep the book for 24 hours before returning it; this helps Montag to feel more comfortable keeping it. Beatty also hints that he himself went through a crisis of sorts before he was able to come back to work and be content with what he was doing. This also makes Montag feel a bit better about his recent "breakdown" and gives him a chance to think about it a bit more clearly. However, Beatty gave him that comfort with the intent that Montag would come back; unfortunately, he doesn't. Then, when Beatty eggs him on in the firehouse, it seals Montag's rebellion; Beatty pushes him over the edge.
By giving Montag history, information, things to think about, and some breathing space, he pushes Montag into realizing just how unhappy he has been, how miserable his society is, and that he doesn't feel like he can keep being who he has been. Although that might not have been Beatty's intent, Montag turns out to be a crusader for revolution.