"Think of it this way. Would you agree that the world has both whos and whats in it?"
"That's pretty obvious."
"And would you also agree that a who is greater than a what?"
"What do you mean?"
"For one thing, a what can make a what, and a who can make a what, but only a who can make a who."
"That seems true."
"Now put those two points together. If only a who can make a who, and the world includes whos, then only a who could make the world."
Stolen from here.