"The Business of Greatness" joke

When Abraham Liebowitz got to school, he discovered that he was the only Jewish kid in the class, but it's a decent town and nobody really bothered him.
One day, the teacher asked the class, "Who was the greatest person who ever lived, and why?" To make it interesting, she held a twenty dollar bill in the air and said, "Whoever gives the best answer will get this twenty dollars."
All of the kids called out their guesses.
One said, "George Washington, because he was the father of our country."
"That's excellent," said the teacher.
Another said, "Abraham Lincoln, because he freed the slaves."
"That's also good," said the teacher, reluctant to bestow the reply of 'excellent,' but still being polite.
One little girl said, "Joan of Arc, because she saved France."
"Another excellent choice," said the teacher.
Then Abraham Liebowitz raised his hand, so the teacher called on him. "Abraham, who do you think was the greatest person who ever lived, and why?"
Abraham said, "Jesus Christ."
The teacher was shocked. "Abraham," she said "I'm very surprised. Class, I think we can all agree that Abraham should get the twenty dollars," and she handed Abraham Liebowitz the money.
At recess, the teacher was still very impressed, so she asked Abraham why he said Jesus:
Abraham said, "Look, personally I think Moses was the greatest person who ever lived, but business is business!"