what is the final commentary by Bradbury on the future of mankind

Granger refers to the lessons of history indirectly in two ways. He talks fondly of his grandfather, from whom he took the lesson that one must strive to contribute to the world and leave something behind. He also talks of the mythical phoenix and how it continually burned itself and was reborn, only to make the same mistake again and again for lack of memory. Society has taken after the phoenix. After the city is destroyed, those left along the tracks set out to rebuild it. There is hope in this, as these are men who mind the lessons of history. The book concludes with Granger, Montag, and his newfound friends walking toward the destroyed city. Hope for the chance to build a new society and hope for the future of man burns bright in the hearts and minds of these men.