What is the significance of Piggy's plea to join the expedition in Lord of the Flies?

In the first chapter, when Ralph, the newly appointed
chief says they need to see if they are indeed, on an island, and therefore they need to
explore, Piggy says he wants to go with Ralph, Jack, and Simon.  Ralph tells Piggy that
he's no good on a job like this; Jack just says, "We don't want you." The significance
is that Piggy is the voice of reason and intellect - a voice needed among the boys. 
Piggy does not get any respect from Jack and even Ralph is slow to show him much,
but Piggy wants and deserves respect.  Piggy even tries another tactic by telling Ralph
that he was hurt that Ralph told the boys his nickname was "Piggy".  Ralph makes Piggy
feel a little better by telling him it could be worse, and that it was Piggy's job to
get the names of all the other boys.  This shows that Ralph has empathy for Piggy, the
sign of the civility which the reader sees in Ralph throughout the
story.