Bodhidharma and the Emperor

Zen and Dao picked out a koan for homework this week (link and text courtesy of Zen):

http://www.enotalone.com/article/6000.html

Emperor Wu of Liang asked the great master Bodhidharma,

"What is the main point of this holy teaching?"

"Vast emptiness, nothing holy," said Bodhidharma.

"Who are you, standing in front of me?" asked the emperor.

"I do not know," said Bodhidharma.

The emperor didn't understand. Bodhidharma crossed the Yangtze River and went to the kingdom of Wei.

Later, the emperor raised this matter with his advisor, Duke Zhi. The advisor asked,

"Your Majesty, do you know who that Indian sage was?"

"No I don't," said the emperor.

"That was Avalokiteshvara, the Bodhisattva of Compassion, carrying the seal of the Buddha's heart and mind."

The emperor felt a sudden regret and said, "Send a messenger to call him back."

Duke Zhi told him, "Your Majesty, even if everyone in the kingdom went after him he wouldn't return."