In the Zen experience, a certain unity happens, subject and object become one, and we come to realize our own self-nature. This self-nature cannot be seen, it cannot be touched, it cannot be heard. Because of these characteristics, we refer to it as "empty" (in Japanese, ku) but its activities are infinite. So, we say the Zen experience is the realization of the empty-infinite of our self-nature or our essential-nature, as it is often called. When this happens, the fact is accompanied by a great peace of mind. At that moment, we feel as though the heavy burdens we have been carrying in our heart or on our shoulders, indeed all over our body and soul, suddenly disappear as if thrown away. The joy and happiness at that time is beyond all words. And there are no philosophies or theologies attached to it. Yamada Roshi