The choice of the word "passions" is particularly important, as is the personification of that word with the imagery of wings. What is happening on the island is the degeneration of human nature. The boys are rejecting what they have learned from civilization and are returning to a more primeval state - more like animals. That is why Golding uses the word "wings" to call to mind animal behavior. By becoming more like animals, the boys are responding more to their desires, their passions, and less to their reason and logic. These passions are "awful" and they "beat" like the beat of the boys' heart. They are ever-present. And the louder they beat, and the more the boys respond, the less like a civilized they become.
Simon is one of the only boys on the island intuitive enough to recognize what was happening to the boys and their rudementary civilization. These intuitions were the "passions," and he was best able to digest them entirely when he was alone--on a mountaintop, in the forest, on the beach. Just as with anyone who is different or plagued with a deeper understanding or intuition (psychics, for instance), they tend to come to the bearers with mixed blessings. They are both wonderful and terrible...gentle and awful wings.
So, as Simon understands, he is equipped to explain to the boys what is happening. As he understands, he becomes a threat--and he is not just the person able to educate about the beast, he becomes as feared and hated as the beast. Before he is able to do any instruction, he is murdered on the beach and allowed to wash out to sea.
Simon is the only boy on the islan who is caring or concerned about anybody else whereas everyone is busy in doing their own thing. Jack wishes to hunt, Ralph wishes to survive and be rescued, Piggy wishes to be accepted and heard and everyone else wishes to do what they feel like. When Simon picks up the glasses, he is radiating with generosity and goodness while standing among a quarrelling group of boys losing their touch from civilization and moving towards evil. The "passions" are represented by each person's wishes and preferences and they "beat about Simon" with awful and evil wings like the animals they are becoming.