Certainly, the Armageddon-like scene of the city's obliteration by multitudes of fires is symbolic of the self-destructiveness of despotic governments and controlling societies. When this happens Granger alludes to the phoenix of mythology, hopeful that civilization will rebuild itself. When the bombing of the city occurs, part of the Book of Ecclesiastes and Revelation comes to Montag's mind, and he recites it over and over. The men go to the river, where life begins. "Montag felt the slow stir of words, the slow simmer."
The "simmer" that Montag feels is that of rebirth in a new world that he and his new-found community must construct from the ashes, much as the phoenix rises anew from his ashes, as Granger has mentioned. With this final scene, Ray Bradbury ends his dystopian novel on an optimistic note, typical of him. Bradbury entertains the hope generated by a spiritual rebirth, what critic David Mogan calls "joyous absorption in the experience of living."
In Fahrenheit 451, after Montag joins the 'book men', they see the city's destruction by the war. This is one of the most important scenes in the novel. The intelligent men see the destruction of the city by a bomb in a second. They, however, do not feel much loss. Rather, they feel more committed to start a new generation.