Why is the setting of "Lord Of The Flies" important to the plot?

The setting of "Lord Of The Flies" is important to the plot for several reasons. First, because the island is isolated, it forces the boys to create /re-create civilization on their own. Second, because it is so lush, it is like Eden; this is less a plot issue than a symbolic one, but it is important. Third, the practical side of the lushness is that the boys aren't killed immediately (say, by harsh winters). Nor do they have to hunt to survive. They can survive on fruit, at least for a while, and they have spare time and energy to get restless—and they choose to hunt. Finally, and this is more a blend of symbolism and history, there is an expectation of the island as an earthly paradise/vacation site. That's what the rescuing officer means with the reference to Coral Island on the final page.