How are Simon and Piggy vital to the story in Lord of the Flies?
Simon is the most attuned to the inner fears and possibilities being faced by all the boys as they struggle to adjust to their situation. "Maybe there is a beast....maybe it's only us." He understands the feelings of hopelessness, but also urges that action of some sort needs to be taken. "What else is there to do?" Simon is brave and selfless at times, as when he summons the courage to go up the mountain and encounter the beast up close. At the same time, however, his difficulty in communicating his insights and discoveries leaves him unable to express or defend himself, resulting in his death.
Piggy is the intellectual planner, the one who spends the most time trying to rationally analyze the surroundings and construct plans for dealing with it. He recognizes the need for order and respect for organization and communication, as symbolized by the conch shell. "We can use this to call the others. Have a meeting. They’ll come when they hear us..." Piggy is able to verbalize the need for the boys to do what they can to increase their likelihood of being found, and he is able to recognize the deterioration of the sense of order and civility that could have prevented the boys' behavior from descending to the basest of animal instincts. "Life...is scientific....I know there isn't no beast...but I know there isn't no fear, either....Unless we get frightened of people."
Both characters are instrumental as voices attempting to preserve calm and reason in the midst of increasing fear and desparation and willingness to follow the uncontrolled violence of Jack the bully.