To me, the big deal about this chapter is that it is the one where Simon is killed.
At the beginning of the chapter, Simon goes up on the mountain and he sees the body of the dead parachutist. He realizes that this is what they thought was the beast. Thinking that this is important news, he heads down to the beach to tell the others that there is not really a beast.
Down at the beach things have gotten kind of crazy. There is a huge thunderstorm brewing and the littleuns are scared. Jack has his people do their pig killing dance with Roger pretending to be the pig. As they get into a frenzy and the storm gets violent, Simon comes into the middle of the circle. They think he is the beast and they kill him.