Faber says this. The larger context of the quote is as follows:
Don't ask for guarantees. And don't look to be saved in any one thing, person, machine, or library. Do your own bit of saving, and if you drown, at least die knowing you were headed for shore.
Montag has approached Faber because he is increasingly disturbed by the idea of continuing being a fireman and burning books. He now wishes to read books. When Faber says, jokingly, that the answer is to sabotage the firemen, Montag takes him seriously. Faber realizes that Montag is sincere, and so tells him—or warns him—that it is not books themselves that matter, but the knowledge in them. He says that saving books by itself is not going to save society: there is no one magic cure to all social ills. Faber also says that waiting around for salvation is not the answer.
At that point, we get to the quote. Faber means here that we have to be risk takers and proactive: he uses the image of "do your own bit of saving:" in other words, see the drowning person, swim out to save him, and if you die while pulling him to shore, at least you are doing the right thing.
This is good advice because it means participating in solving problems, taking the initiative to help others, and being the change you want to see. This is especially important in a society like Montag's, where everyone is taught to be passive and quietly accept the way the world is while immersing themselves in televised fantasies.