Ling Tse master asks the head zen master “what is the essence of Buddhism?” then the head zen master hit him. Ling Tse master asked the same question again, and was hit again. Ling Tse master asked for a third time, and got hit again.
If we review this Koan, Ling Tse master asks “what is the essence of Buddhism?” the main essence is mind, nothing beyond the mind. When the head master hit him, he showed him that by hitting him, this is a function of the mind from the essence. Being hit is a phenomena manifested from the mind. This is the essence of Buddhism, and the zen master showed him the truth three times. That is the answer to the question.
Everyone thinks the zen concept is so hard, but actually the concept is so humble, practical, and easy. Introspection into your mind is all that is needed, and commit to full responsibility of the mind’s function. Take full responsibility of the function of the mind. All phenomena is from the mind, and once you realize this, you see your nature. It is just that easy.