What do you think this quote is saying" "The world, that understandable and lawful world, was slipping away…”
This quote comes in Chapter 5, where the schism occurs within the group of boys. Ralph is struggling to keep order, in the face of fear (especially among the littluns) of "the beast" and the bigguns' desire for meat and eventually violence. He also argues the importance of keeping the signal fire lit, and maintaining the poorly constructed shelters. In short, he is attempting to hold onto the fragile order and social structure that emerged when the boys were stranded.
Jack, on the other hand, is eager to hunt, to do what in his mind is fun, but is actually a rejection of that fragile social system. He and the other hunters want to break free, to chase pigs, to basically do whatever they want. They deny the responsibilities that Ralph is trying to impart to the entire group. He doesn't want to watch the fire, he doesn't want to build the shelters, and he challenges Ralph's right to force him.
At this point, Ralph asserts that he was chosen as leader, and draws his authority from that. The hunters, however, reject this stance and leave. For Ralph, the world that he knows: adults, control, rational thought, is slipping further and further away. In its place is a world of violence, of lawlessness, and eventually death. This is the moment when Ralph realizes that events are beyond his control, and he will have to focus solely on survival from here on out.