"Once there was a priest who walked in front of the Master (Budai). The latter touched him on the shoulder, whereupon he turned his head. The Master said "Give me a cash." The priest said, "If you first tell me a word of Truth, I will give you a cash." The Master put his bag on the ground and folded his hands." (transl. Helen B. Chapin)
Most people who read this think it's pretty cool. Some Zen students or their teachers imitate it by lifting up their staff then putting it down or by doing other odd things. None of this gets to the heart of what Budai was expressing. When Budai sat his big bag down then folded his hands, in essence, he did the exact same thing as the Buddha did when the Buddha simply held up a flower then blinked and in response to this, Mahākāśyapa just smiled. Both of their actions appear to be physical but both saw what ordinary people could not see, the dynamic universal substance (體) that animated both of their physical functions (用). Does this sound preposterous? Well, it is not.
We always have to keep in might that the Buddha had a very simple and elegant teaching. There is the conditioned reality consisting of phenomena including our bodies all the way to our consciousness. Attach to this and you are in deep doo-doo. You will enter samsara never to escape from it. Then there is unconditioned reality known sometimes as nirvana. No, you cannot see it or sense it. It is beyond the reach and range of sensory consciousness (sorry). It is primary, first, original—we can call it the One Mind (S., ekacitta). In Zen this becomes essence (or if you like, substance) with function as its expression. On this same track, Zen master Hui Hai says:
"This functional manifestation proceeds from the fundamental "substance" and it is by means of it that we return to that "substance". Since "substance" and manifestation are one in reality, the fundamental and its manifestation do not differ from each other."
Back to our rotund Budai. He was continually aware of this unconditioned essence which he called "Mind" which he said is the most intelligent and the most spiritual thing. Budai said of Mind that it is continual movement (i.e., dynamic), moreover, self-existent (absolute) ; and there is nothing which it is not. It is before one's eyes, the true great way, yet one sees not a hair of it—how strange.