Laozi quotes - page 10
There are three layers to the universe. In the lower, Tai Ching, and the middle, Shan Ching, the hindrance of a physical bodily existence is required. Those who fail to live consistently in accord with the Tao reside here. In the upper, Yu Ching, there is only Tao the bondage of form is broken, and the only thing existing is the exquisite energy dance of the immortal divine beings.
Laozi
... These are notions of the mind, which is like a knife, always chipping away at the Tao, trying to render it graspable and manageable. But that which is beyond form is ungraspable, and that which is beyond knowing is unmanageable. There is, however, this consolation She who lets go of the knife will find the Tao at her fingertips.
Laozi