What is the Essence of Buddhism?

At the High Seat, a monk asked: “What is the essence of Buddhism?”

The master raised his fly-whisk
The monk gave a Katsu.
The master hit him.

Again, a monk asked: “What is the essence of Buddhism?”

The master raised his fly-whisk again.
The monk gave a Katsu.
The master also gave a Katsu.
The monk hesitated.
The master hit him.

The master then said: “Monks, some do not shirk losing body and life for the Dharma. As for me, I spent twenty years with my late master Obaku. Three times I asked him on the essence of Buddhism, and three times he kindly beat me. It was as if he had caressed me with a branch of fragrant sage. Now I feel like tasting a sound beating again; who can give it to me?”

A monk stepped forward and said, “I can.”
The master took up his stick and handed it to him.
The monk hesitated to take hold of it.
Then the master hit him.

taken from (attention: link leads to a large PDF file)  The Teachings of Rinzai