The Book of Ecclesiastes, from the Old Testament, is a warning to mankind that Earthly pursuits are futile because all men die, and all accomplishments ultimately degrade to dust; the pursuit of a noble life and teaching of knowledge are greater than all the money or power in the world. Faber, as an ex-professor, knows the power of teaching, but is so scared of death that he has capitulated completely with the rules of the society; he no longer teaches his knowledge, so it will die with him. When Montag meets with him, Faber says:
"I'm one of the innocents who could have spoken up and out when no one would listen to the 'guilty,' but I did not speak and thus became guilty myself. And when finally they set the structure to burn the books, using the firemen, I grunted a few times and subsided..."
(Bradbury, Fahrenheit 451, Google Books)
Too scared to act, Faber's Earthly pursuit -- that of knowledge -- has become futile. It is only after Montag speaks with him that he has the motivation to continue the struggle; like the speaker in Ecclesiastes, Faber knows that if he does not pass on his knowledge, his life will have had no meaning. Faber finally changes, helps Montag escape, and escapes himself to spread his knowledge, thus reasserting the claim from Ecclesiastes that a noble life and the teaching of wisdom is the only Earthly act worth pursuing.