What's the joke of Lu Yu robber Ren Lei?

The Zen master was meditating when he met a thief with a big knife rest around his neck. The thief said, "Take out all your money."

Zen master: "money is a thing outside the body." You can't take it without it. The donor can accept it. "

Thief: "This is your charity for life."

Zen master: "The Buddha said that there is a causal cycle. You and I had a cause in our previous lives, and today's fruit is there."

Thief hair: "I am guilty, can the Zen master cross me?"

Zen master: "can"

Thief: "How to cross the law"

Zen master: "Put down the butcher knife and become a Buddha."

Thief: "Put it down"

The Zen master stepped forward, picked up the butcher knife and pointed it at the thief: "Little X, give me my money back".