In the allegory Plato invites us to imagine a cave in which prisoners have been chained since childhood. Behind them is a fire and between the fire and the prisoners there are men walking back and forth carrying burdens. The fire casts shadows of these men on a wall which the prisoners have all their lives been facing.
One prisoner, however, is released from his chains and dragged up and out of the cave where he beholds the world in the light of the sun. At first he can scarcely open his eyes, accustomed as they are to the darkness, but gradually he's able to see that a world that's infinitely richer than the world of the cave.
He won't believe his eyes but gradually he realizes that the world of the cave is all illusion, that the world he sees in the light of the sun is the true reality.
He would take pity on his comrades still chained in the cave. He would care nothing for the honors they value. He would count it all so much empty and meaningless chatter. All that would matter to him is the brilliance of the sun and the beauty and variety of the world.
He might even return to the cave to tell his fellows what he has seen, but they wouldn't believe him. They'd think he'd lost his senses, and if he tried to persuade them to join him outside the cave they may even kill him.
Plato's parable works on many different levels. For Plato the man who escapes the cave is the philosopher who escapes the realm of darkness and shadows and apprehends the world in the light of the Good, the Beautiful and the True. When the philosopher returns to the cave to seek to enlighten his fellow prisoners they refuse to listen to him and, perhaps like Socrates, he may even be put to death.
For Christians for two thousand years the cave represents the present world with its empty and meaningless pursuits and illusions. The sun is the absolute Good, Beautiful and True, i.e. God, and the world illuminated by this "Sun" is the really real.
When the "prisoner" seeks to persuade his fellows that they're wasting their lives debating about shadows when there's a beautiful, meaningful life awaiting them outside the cave, they often think he's gone insane, and, as has happened to millions throughout the last two millennia, they may even kill him.
Plato's allegory of the cave has endured for 2300 years because, whatever his original intent, it neatly captures a deep truth about reality and the human condition.
