Timmy: "Hey, Mr. Will. What's God?"
Will: "That's a good question. I suppose that depends on who you ask."
Timmy: "I'm asking you!"
Will: "Alright, I'll tell you. Do you ever play with toys, Timmy? Maybe little action figures, legos, and trucks?"
Timmy: "Of course."
Will: "When you play with legos and trucks and things, do they act like trucks or people?"
Timmy: *thinking* "What do you mean?"
Will: "When you're playing with the toys, do they talk and think like people?"
Will: "Why do you think that is?"
Timmy: "I dunno. Why?"
Will: "People —human beings— are social. We have to team up in order to get things done a lot of the time. Most of the time, throughout our history, we've lived in groups of people, not alone. Think back to what you learned in school about cavemen. They lived with family and friends, and everybody had to help out just so they could survive."
Timmy: "Like Democrats!"
Will: "You got it. Well, because we had to all work together so much, people had to learn really early how to understand other people. It's hard to communicate and get something done if you don't understand the person or people you're working with. Well, this skill grew in humans very early. And the better people were at understanding other people, the more likely they all were to survive. This became a survival trait. Before too long, most if not all people were pretty good at sympathizing with other people, understanding other people's thought processes, and using teamwork to get things done. And we were really successful. We spread out of a small place in Africa into the Middle East, then South Asia and even Europe. Before too long, we were the dominant species on the whole planet."
Timmy: "Cool. But what does this have to do with trucks?"
Will: "Because humans were so smart, we were always trying to learn and understand everything around us. The problem, though, was that we didn't have thousands of years of science to build on like we do today. There's no way a hunter-gatherer from 8,000 B.C. could understand that the sun was made up of a nuclear furnace, burning hydrogen so hot that it turns into helium, nearly 100 million miles away. How could they? Astronomy was still in its infancy, and nuclear physics wouldn't be along for nearly another 10,000 years. But that didn't stop them from being curious... so they guessed. So how do you think they explained the sun?"
Timmy: "I dunno."
Will: "They did what they'd learned how to do over thousands of years; they gave it a personality."
Timmy: "But the sun's not a person! It's a fireball!"
Will: "You know that and I know that, but they had no idea. All they saw was a warm ball that rose and fell every day, and they knew it was very, very important. The knew the sun was necessary for warmth, for growing crops, for telling when the harvest season was going to end, and even just telling what time it was during the day. The sun was important! So what happens when you combine these? What happens when you combine a great physical force with a personality?"
Will: "Basically, yes. They figured that this very, very powerful personality was something to revere, so they started worshiping the sun. And because the sun isn't consistent — some days are hot, some days are cold — they assumed that their behavior could influence the sun god. Appeasing the sun god was thought to have positive results and angering the sun god was thought to have negative results."
Timmy: "But that's not how it works. The sun does what it does because of other reasons."
Will: "You're absolutely right. Because of that, the response to their praise and worship wasn't consistent. You can pray to the sun one day and have it sunny, and you can pray to the sun and have it cold the next. This is when something pretty bad happened. Because people thought they could communicate with the sun, they thought that somehow that gave them a supernatural importance, and people got kind of addicted. The people that were the most addicted became priests and shamans. These were spiritual leaders that were expected to be authorities on what the sun wanted or how the sun thought. As time went on, other natural phenomena were also given personalities, and eventually they were just assigning gods to whatever. There were wind gods, ocean gods, mountain gods and sky gods. And then people with one set of gods would meet other people with another set of gods. This generally didn't go very well. Inevitably one group would try to convert the other and they'd either succeed or they'd both fight."
Timmy: "That's stupid!"
Will: "We're still doing it today, though."
Timmy: "Wait, I mean the Christian God."
Will: "I'm getting to that. Eventually, it was the gods and not the phenomena that were important to people. God wasn't the sun god, Ra, anymore, it was king of the gods Zeus, for example. Zeus did throw lightning, but that wasn't why he was praised anymore. Then came the Jews."
Timmy: "Like Jon Stewart?"
Will: "Sort of. Around 2000 B.C., a man named Abraham had a vision and thought he saw angels. He was scared, but because he got his wife pregnant he believed it was true. He gathered together old myths that had been handed down from some of his ancestors and then started a religion that we now call Judaism. He passed down the religion to his sons, and they added a bit more, and then their sons added a bit more. Before long — maybe 600-700 years — they had a lot of followers. They were all over the area we now call Israel. Anyway, they ruled for a while and were conqured a few times. One of the best ways to keep people believing in a religion, they and others found, was to make vague prophesies. These were just guesses about what might happen. If they came true, and they usually did because they were so vague, they could use that as evidence that their faith is real. Anyway after a while, according to Christianity, a man came along. His name was Yeshua bin Joseph but most people now just call him Jesus or Jesus Christ."
Timmy: "Jesus Christ!"
Will: "Yes. This part is a bit of a mystery, because we're not really sure if there was a real Jesus or not."
Timmy: "What?! Why?"
Will: "The thing is, they didn't start writing the Bible until like 70 years after Jesus was supposedly born. And the accounts of Jesus' life aren't consistent going from author to author. The worst part is that evidence outside of the Bible that we have now usually came from the Bible at one point or another or was made up. We'll probably never know for sure if he was real or just a combination of other religious figures."
Timmy: "So god is just people believing in nothing? Wait a second, we already know about how the sun works, though. We know how a lot of things work. Why do people still believe in god?"
Will: "A few reasons. First, when you're really little, you tend to believe what your parents and other adults tell you. It's another survival trait. Back in the caveman days, if your mother told you to stay away from wolves, you had better stay away from wolves. Those kids that didn't listen were probably delicious, and they were eaten before they could reproduce. Another reason has to do with the way people interact. There's something called groupthink. Because humans have done so well when we cooperate, it's become a part of us to want to cooperate, to get along with and agree with others. Unfortunately, sometimes this can go too far, and we'll agree with a group of people even if what you're agreeing with is bad or doesn't make sense. But the big two reasons are easy: the carrot and the stick. Smarter animals, like humans, can be conditioned through rewards and punishments to do and think pretty much anything. In religion, generally there is a promised reward for believing and a stern punishment for not believing. Ask a christian about hell if you want to know about their punishment. It's basically torture for all of eternity. Pretty scary right?"
Timmy: "So they think you're going to be tortured forever?"
Will: "Most of them do, yes."
Timmy: "Why don't you believe?"
Will: "I'm not afraid of something for which there's no evidence and I'm not motivated by something for which there's no evidence. It's that simple."
Found here, thanks, with minor modifications.