One of Golding's major points in writing the novel was to demonstrate that the view of man as an idealistic creature was a faulty one. He was particularly interested in demonstrating that no amount of "civilization" could change the underlying human tendency or capability of violence and murder and destruction. Removing the boys from their world was an important step in demonstrating how this would play out.
When Jack says "We're not savages. We're English, and the English are the best at everything," he is bringing up the thesis that Golding will prove wrong with the story that follows. The boys themselves share this false perception of the nature of man that they will abide by rules even when the mechanisms for enforcing those rules have disappeared.
As the story progresses, the boys become more and more savage, first killing by accident and then on purpose as they forget more and more of the rules of the civilization that they left behind. The island in its darkness and mystery, the ocean in its violence around castle rock, the fires the boys light, even the weather all signify the idea that civilization is an illusion, a facade that takes very little to break down.
The theme of rules in society placed to create order is central to the novel Lord of the Flies. At the beginning it is shown how the boys still think it is important to keep order since they are "English". They emphatically remind themselves "We've not savages" and try to imitate the ordered English society they came from. However, as the novel progresses more and more order breaks down being replaced slowly with an all consuming chaos. With this novel Golding is trying to make a point about society and its rules. Through the boys in Lord of the Flies Golding shows how we only follow the rules because we are taught that is the way to behave. At the core of human nature is savagery and an instinct for primal dominance and a disregard for logical rules. This theme can be observed and analyzed throughout the novel.