Fire has incredible importance to our species. It is no coincidence that many cultures consider it divine (or a gift from the gods). It does, after all, represent a major separation between people and animals. Anthropologists believe that the invention of language closely followed our species' ability to produce fire, as having light in the evenings created the space for nascent culture. Cooking food, too, separated us from other animals, and was impossible before we could consistently produce fire.

In The Road, "carrying the fire" represents carrying the seeds of civilization. The father and his son don't break the most sacred rule of civility: people don't eat each other. Animals do this; people don't.

The other bandits on the road are usually cannibals. They represent further destruction of the world that once was—bringing people back into their beast-like, animal state. They prey upon each other. By contrast, the father and the son carry the fire. They represent hope. They would starve rather than become animals.

It's worth noting that McCarthy uses a similar symbol in both Blood Meridian and No Country for Old Men.

The phrase "carrying the fire" comes up four times in Cormac McCarthy's The Road and is said eight times in those four scenes. It also appears as "carry the fire" in the scene where the man dies. Carrying the fire signifies hope for the human race; though the world seems all but over, as long as someone is alive and trying to thrive, they're still carrying the fire, which means the human race still has hope.

When the boy is scared early in the novel, his father assures him that they will be okay. When his father agrees nothing bad will happen, the boy says, "because we're carrying the fire." His father affirms this, saying "Yes. Because we're carrying the fire."

The next time the phrase appears, it's after an encounter with cannibals. The man promises the boy that they won't ever eat anyone. He says they're the good guys and that they're carrying the fire. That light for humanity means that they can't turn their back on being the kind of people who don't exploit others and eat them for food.

The third time the boy says the phrase, he's asking his father about the possibility of finding another father and son like them. He says, "And they could be carrying the fire too?" The man assures him that it's possible but that they can't be sure. He's trying to teach his son to be wary without extinguishing the hope that there are still good people in the world.

When his father dies, he insists that the boy has to go. He charges his son with carrying the fire. He tells him:

You have to carry the fire.

I dont know how to.

Yes you do.

Is it real? The fire?

Yes it is.

Where is it? I dont know where it is.

Yes you do. It's inside you. It was always there. I can see it.

In this way, his father shows that the fire isn't a real fire. Rather, it's the drive that keeps humanity going and the hope for a better world.

The boy accepts what his father says and goes with the man at the end of the novel. He asks the man whether he's carrying the fire—the fourth and final time the complete phrase appears—and the man doesn't understand what he means but finally says that, yes, he's carrying the fire.

The boy goes with the man.

The "fire" in this text is a very important symbol of both hope and humanity. McCarthy presents the reader with a grim and relentless dystopian world which offers little hope or future for humanity. The remnants of the human species are forced into cannibalising each other merely to survive or scavenging for tins and other dried goods thanks to some kind of unspecified disaster that has overtaken the planet. As a result, the humans in the book are presented as shadows of their former selves, debased and animalistic in the way that they prey on each other and have lost any sense of moral code. It is only the father and the son in this text that offer some kind of hope for humanity, and it is this that is captured in the phrase "carrying the fire." Note how this is directly addressed when the father realises he is dying in the injunction he gives to his son:

You have to carry the fire.

I dont know how to.

Yes you do.

Is it real? The fire?

Yes it is.

Where is it? I dont know where it is.

Yes you do. It's inside you. It was always there. I can see it.

In the father's description of the fire, it is clear that the way he talks about the fire being "inside" his son, and "always" being there, is something that points towards its symbolic meaning. The fire that the boy is told to continue carrying represents the hope for humanity. This is why when the boy meets the man who will take care of him he instinctively asks whether he carries the fire. As long as this symbolic "fire" burns, there is still hope for the future of humanity in this grim world.