Our thoughts are one thing but getting down the the essence of thought is quite another matter. Most approach Zen never thinking that its goal is to get to the very stuff of thoughts. In this regard, it really doesn’t matter what thoughts or concepts we play with. The goal remains the same, to get to the essence of thoughts. Supporting this, the Sixth Patriarch Huineng said: “True Reality is the substance of thoughts.”
But rather than go this far, the curious and Zen practitioners prefer to think about Zen, that is, to understand Zen only at the level of thought—not going deeper to the very essence. So they buy a collection of koans such as the Blue Cliff Records or the Mumonkan and read these koans over and over for years.
When these people look into their noggins during zazen or just walking trying to figure out a koan they seem to always draw a blank. They don’t realize that what is going on between their ears is like a vast restless ocean. It’s all unceasing waves, that is, unceasing thoughts. If these thoughts were to cease, suddenly, in about the time of a finger snap they would see the essence. Moreover, they would discover who they really are.
"Successive thoughts do not stop; prior thoughts, present thoughts, and future thoughts follow one after the other without cessation. If one instant of thought is cut off, the Dharma body separates from the physical body, and in the midst of successive thoughts there will be no place for attachment to anything” (Sixth Patriarch Huineng).
This Dharma body is the essence or stuff that thoughts are composed from.
Unfortunately, there are a lot of people who have a copy of the Blue Cliff Records and the Mumonkan and believe that all these koans have nothing to do with seeing the essence of thoughts. But where does such a belief lead? What do such people think Zen is about? All that I can say is such people are stuck on words and the thoughts which arise from going over words. They harbor certain concepts about Zen which are hard for them to give up.