The opening lines of the novel in Part 1 show Montag's joy in his job:
It was a pleasure to burn. It was a special pleasure to see things eaten, to see things blackened and changed.
As a "fireman," one who ignites and feeds fires rather than put them out, Montag has pride in his job because he has never thought differently. He does not see the fires as destructive, but constructive, keeping the status quo of society intact.
From Part 2, Montag imagines Beatty telling him to burn his hoarded books:
"Light the first page, light the second page. Each becomes a black butterfly... chainsmoking, chapter by chapter... all the second-hand notions and time-worn philosophies."
It is hinted throughout that Beatty is a reader, as are the upper-government bodies. Beatty has a way with words, and draws from literature, creating images that inspire emotion, such as his comparison of the burning pages to a "black butterfly," each page becoming ash as it burns and is destroyed forever.
From Part 3, Beatty confronts Montag at last, and shows that he suspected Montag for a long time:
"Old Montag wanted to fly near the sun and now that he's burnt his damn wings, he wonders why."
(Bradbury, Fahrenheit 451, Google Books)
The reference is to Icarus, who flew with feathers and wax but ventured too close to the Sun and died. The Sun, the most powerful fire in the Solar System, is the ultimate example of constant destruction that in its fury creates life; without the Sun, the Earth would be dead. Montag, discovering the joy of reading and the vastly superior ideas in books versus television, had no self-control, and instead of burning the books, he burned his own boundaries. Beatty thinks that he can still return to "normalcy," but underestimates the power of the reading fire that has been ignited in Montag.