What is the significance of Simon in the first four chapters of Lord of the Flies?how does he highlight the evil in others? what does he do to...

We are first introduced to Simon as the boy who faints. 
Golding is playing on the idea that Simon is epileptic and therefore, according to
ancient beliefs, somewhat psychic.  This prophetic trait is emphasized later when Simon
tells Ralph that "you will get back all right."  On the first expedition to explore the
island, Simon is the one to recognize the candle buds.  Unlike Ralph and Jack who see no
value in something that cannot be used or eaten, Simon just likes them for their aroma. 
This closeness to nature is also emphasized throughout the novel as Simon retreats to
his bower and lets the beats of  his heart match the rhythms of the waves (end of
Chapter 3).  In Chapter 3, Simon is the only one who stays with Ralph and helps him
build shelters.  The others all desert him.  In the same chapter, Simon's kindness is
also reflected when he picks fruit for the littluns who cannot reach it on the trees. 
In Chapter 4, he  gives Piggy his share of meat when Jack refuses to give Piggy his
portion. 

To get an idea of how Simon's goodness is
contrasted to that of the others, especially Jack, read the opening of Chapter 3 in
which Jack is described in detail.  Then read the closing of that chapter in which Simon
is described in detail.  Simon's kindness, thoughtfulness, posture, relationship with
nature are consistent with that of a Christ figure.  Jack's obsession with hunting and
 his animal-like posture reflect that of a savage.