This is a great request. Here are some ideas that will help you get started.
First, you can argue that the island is like the Garden of Eden. Moreover, you have boys, who are relatively unspoiled by the world around them. For this reason, there is a sense of innocence or nature in its pristine form.
Second, based on this premise, you can argue that there is something called original sin, as the boys at the end are after each other even to do each other harm. Two characters even die in the novel.
Third, you can say that without the strictures of society, there will be chaos and anarchy. From a symbolic level you can point to the breaking of the conch, which points to the overthrow of order.