Simon's first introduction was the person who fainted, which suggests he had epilepsy. The reader understands he's delicate .
Simon represents a chirst like figure because of his kindness for others- "Simon found for them the fruit they could not reach, pulled up the choicest from up the follage"- he is a provider.
He is the most perceptive about the beast. He says "maybe there is a beast... What I mean is... maybe it's only us". He is the only one to see that the problems on the island stem from the boys' relationships with each other, not from an outside force. Yet nobody understands what he's trying to say.