Apart from Clarisse, Professor Faber may be the most important influence on Montag in the novel. He guides Montag through his transformation, encouraging the protagonist to explore the books he's recovered. At one point, Faber gives Montag a transmitter that fits in his ear, so that they can have continuous communication. Unfortunately, Montag becomes overconfident and begins behaving recklessly, reading poetry to his wife and her friends, despite Faber's warnings.
Shortly thereafter, Montag is called to burn his own house. During the confrontation, Captain Beatty discovers the Seashell (transmitter), and Montag kills him and flees. He runs straight to Faber, who sets him on a path to freedom from society. He introduces Montag to a group of outsiders who hold great works of literature alive in their minds. One might argue that Faber, along with Clarisse, "saves" Montag from the crippling alienation and isolation of the society in the novel.
Professor Faber can be seen as the beginning of Montag's gradual disillusionment with the society he lives in. Long before Montag meets Clarisse, he encounters an old professor in a park who gives him his very first glimpse into the world of books, knowledge, and thought. Later on Montag meets Clarisse, and when he becomes determined to find out more about books, he seeks Professor Faber. Faber is very important in that he contributes some organization to Montag's thoughts and plans. When Montag seeks out Professor Faber, he has no idea what he is looking for or what he's going to do. Faber provides Montag with material, with books, and teaches him how to interpret them. Faber also gives Montag more solid plans, more realistic schemes that might uproot the horrible society they live in. Faber also becomes a source of strength for Montag by giving him a device through which Faber is able to speak to Montag and guide him as he confronts Beatty and finally breaks away completely from the society they both hate.