I have to write an essay on power and change and i need help explaining it.

If there is one theme that unites these symbols (although I would caution against calling Jack a "symbol"), it is power to dominate others with the unknown. Jack claims to have knowledge of "the beast," which frightens the others into joining his tribe. The conch shell is supposed to signal a meeting, which implies that there is something important going on. Finally, Piggy's specs represent the ability to see things that others cannot see.