Explain the importance of the quote youre not wanted we are going to have fun on this island so dont try it on my poor misguided boy or else

In a more symbolic sense, the pig's head represents evil
incarnate, temptation.  We know that from Golding's notes on the novel in which he
equates "Lord of the Flies" to Beelzebub. On the other hand Simon has striking
similarities to Jesus.  He is kind, compassionate, intuitive, prophetic, and messianic.
 The pig's head acts as his tempter, equivalent to Satan's temptation of Jesus in the
wilderness.  What Simon is being asked to do is "have fun on the island."  This phrase
is most often used by Jack, and to him "having fun" means hunting and killing.  Almost
every other boy on the island with the exception of Piggy enjoys the savage nature of
the hunt.  Even Ralph enjoys participating in the boar hunt, and later engages in the
pig-hunt reenactment, which almost goes too far--Robert acting as the pig is almost hurt
by the boys surrounding him.

Simon is asked to join in the
fun or savagery.  In order to survive on the island, he must change.  The consequence
for remaining civilized is death.  As the pig's head tells Simon, the boys "will do him"
if he does not "play."

It is not Simon's nature to change,
to become savage, to hurt, or to kill, and he resist this temptation by falling into a
fit.  When he comes to, he goes to tell the boys the true nature of the beast. This
action leads to the fulfillment of the pig's head's prophecy.  The boys do indeed "do
him."