In Ecclesiastes, a lot of its main theme focuses on how worldy pleasures, vanity, material goods, and worldly pursuits are worthless, meaningless, and empty. Pursuing the world, filling your life with pursuits of money and pleasure will leave you without anything of real import in the end. That theme represents the society that Montag lived in, and how it is empty and meaningless, despite its full and busy schedule as it pursues worldy pleasures. That is a significant book in the bible, and Montag memorizes it, and becomes its guardian as they go to help rebuild the city. It contains important lessons on how to rebuild a society that is based on real, meaningful values instead of emptiness.
"Dover Beach" is also symbolic of their society. It talks about how faith used to be full but is now "retreating, to the breath of the night wind" leaving only "naked shingles of the world" and how this life has "neither joy nor love nor light" anymore. It's a great representation of what their society has become. Faith, love, and real meaning are gone, and they are left alone, and they must "be true to one another" at the end to rebuild and survive. As Montag quotes this poem to the women, they are very upset when faced with the truth it presents them, and is symbolic of the sadness that exists in their society.