What does this line mean?

Faber says this to Montag. It is a reflection of how their society operates. The "cattle" are the masses of people who accept the "truth" shoved in their face at face value. The masses neither question nor rebel. They stand "solid" and "unmoving" in their ignorance. Captain Beatty personifies this and is even more dangerous than the average person. Faber explains that Beatty has formed a philosophical and moral justification for all that they are supposed to believe in. It is people like Beatty who keep the ideological fences strong that trap the masses in ignorance.