This passage comes after Montag has killed Beatty and has managed to escape, with Faber's help, across the river. The silence refers to the atmosphere of the campfire with the men (the book covers) around it.
The reason that it is a silence is that the men are at peace, I believe. In the city, no one was at peace. They were all trying to do stuff, to listen to the parlour walls or to go out and speed around in their cars or something. But they were never just quiet and thoughtful like these men are.
It is concerned with all the world because this is the sort of thing that all the world needs. It needs to have this kind of opportunity to be quiet and think.