Symbolism -- it gives deep shades of meaning to even the most mundane everyday objects and events. In Sir William Golding's Lord of the Flies, symbolism is used at every turn of every page, from the largest and most influential events, to something as small as a pair of glasses. Piggy's specs represent intelligence and civilization, hope and security, but they also mark the boys' gradual degeneration towards savagery.
First of all, the specs represent knowledge and the society that the boys came from. In literature and other forms of expression, one with glasses is thought of as studious and smart. For an example, look no further than the spectacled figure of Professor Dumbledore in the Harry Potter series. This wizened character shows great wisdom and intelligence in the novels. And the spectacled Piggy in Lord of the Flies has those traits of knowledge that his archetypal lenses suggest. It is Piggy who suggests using the conch shell found by Ralph to call the others, and it is he who tries to keep order on the island and working to establish civilized society on the island.
More importantly, the glasses are symbolic of hope. Piggy's specs are what the boys use to light their signal fire, and without the fire, there is no hope for them of ever being rescued. Thus, the only hope the boys have to be saved is in Piggy's lenses, and even the glasses themselves hold within them that same hope of leaving the island. Their lives and future hinge on keeping that fire going through the help of the specs.
However, the fate of these spectacles mirrors the fate of the boys during their descent into savagery. During the confrontation between Jack and Ralph atop the mountain, after a ship had passed when the fire was out, fighting ensues, and one of Piggy's lenses is shattered. This simple act of destruction symbolized the shattering of decency and civilized actions. While not completely gone, the destruction of civilization begins, and now the boys begin a downward...