Li Daochun on the "Mysterious Barrier"

This short passage is translated from the Zhonghe ji (Anthology of Central Harmony), a work containing writings by Li Daochun, who was active at the end of the 13th century. The passage is part of a conversation between Li Daochun and one his disciples.

The scriptures on the Elixir say that the wonder of the practice essentially lies in the Mysterious Barrier (xuanguan). I don't know where exactly is the Mysterious Barrier.

Li Daochun said: The Mysterious Barrier is an utterly mysterious and wondrous function. How could it have a fixed position? If it is situated in the body, this is not correct. If it is separated from this body and is searched outside of it, this too is not correct. Those who are mired in the body situate it in the physical shape; those who are mired in the outward situate it in the external things. In any case, the Mysterious Barrier is the place where the Four Elements and the Five Agents do not cling.

(The Four Elements of Buddhism are Earth, Water, Fire, and Wind. The Five Agents of the Chinese tradition are Wood, Fire, Soil, Metal, and Water.)