Woodworker Ch'ing has carved a bellstand of such beauty that a marquis asks if he possesses some special spiritual power. Ch'ing replies that no, he just joins heaven to heaven.
Increasingly, I see how the relationship between the human and the heavenly (nature) was a central concern of Chinese philosophy of the time. This is in part because it continually emerges as a 'problem' for me as well, as I attempt to understand their thought and how it might inform my own.
Perhaps a good place to start when discussing this philosophical "knot" is to put it in the larger context where it is recognized as primarily a cognitive knot, and not one that life itself does not naturally untangle. Ch'ing creates the bellstand, not because he has intellectually untangled this knot, but because he has lived his creation in such a way as to obviate any need for discussion about where nature ends and the human take over. But others want to know how he does it, and thus he must resort to words.
The knot is this: All things are Nature (Dao, Heaven). The human is therefore also, in its every expression, Nature. But the human seems capable of being other than Nature, both in its positive creation of bellstands and in its negative deviations of alienation from Nature and itself. This latter is the moral sphere. Nature knows nothing of right and wrong. Humanity is steeped in right and wrong. Why? Because it recognizes its freedom to deviate from Dao. Humanity both is and is not Nature. But the "is not" can never deviate from "is" — humanity at its most deviant is Dao (where "deviance" has no meaning).
Zhuangzi resolves this problem by declaring it unresolvable. Not only this knot, but every cognitive attempt to explain reality, is intellectually unresolvable. But not to worry! he shouts, life requires no resolution; let it live in and through you and leave the "understanding consciousness" to answer the more limited questions that belong to its sphere. For Zhuangzi, "untangling the knots" is to allow them to untangle themselves in the spontaneity of living.
This is something which his interpreters and other voices in the Zhuangzi are largely unable to do. They fall back into the natural human inclination (which, in this extreme, Zhuangzi would see as a deviance — trying to know what cannot be known) of needing to explain and resolve things. The author of the 17th chapter tells us definitively that Heaven is that oxen and horses have hooves, while putting a hole in the nose of oxen and halters on horses is of humanity. Heaven is Nature; humanity is that which changes Nature. We are enjoined there, and throughout the other chapters, to only follow the Heavenly. That this simply tightens the knot, seems to escape them.
You can check out Scott's writings on Zhuangzi here.