Case 32: Jo and the "Essence of Buddhism"

A senior monk Jo asked Rinzai, "What is the essence of Buddhism?"
Rinzai came down from his seat, grabbed him by the lapels, slapped him and
thrust him away.  Jo stood there as if rooted to the spot. 
A monk standing nearby said, "Senior monk Jo! Why don't you make a deep bow?" 
As he made a deep bow, Jo suddenly attained a great enlightenment.