"It was a pleasure to burn" in the beginning is when Montag feels no shame for burning books.
At this point Montag is really thinking about what Clarisse said. Montag says to himself that he isn't happy with the way he is living.
When Beatty comes to Montag's house to talk about the crime. Montag tells Beatty "and me not sleeping tonight or tomorrow night for a long while, now that this has started." Trying to explain to him how bad he feels.
Montag eventually runs into this man named Faber who has kinds of knowledge and starts to tech Montag. While Faber is trying to explain to him, Montag gets really interested, and is even asking him about the bible.
Montag finally realizes the true meaning of knowledge and goes against the whole society. When Montag is sent to burn the books he is secretly keeps them & hides "behind the grill".
Towards the end Montag has moved away from the city to a small community with a group of people who dedicated to memorizing books. For the first time ever Montag has a life to look forward too.