For the title of the sixth chapter of the Zhuangzi Ziporyn translates "The Great Source as Teacher" and Mair has "The Great Ancestral Teacher". In both cases we are directed to 'that' from which all things originate. Since all the titles of the Inner Chapters are almost certainly the additions of a later editor, we should not take them as necessarily how Zhuangzi himself would have summarized this (again likely editor created) assemblage of his writings.
A great deal of what Zhuangzi is saying here does, however, direct us to consider the implication of an unknown Source and to allow this to teach us how best (most happily) to engage in the life experience. The guiding principle in this is that despite an undeniable sense that there is a Source, we cannot honestly say anything about 'It'. Even to say that 'It' is, is saying too much. "The [Dao] has a certain realness and reliability to it, but no deliberate activity and no definite form." (6:30; Ziporyn) It is this double-edged sword of there seeming to be a necessity on the one hand and a total lack of the definite on the other that makes this experience so poignant. It is very much like emptiness, a something that is nothing. And it is in this that the human experience is rooted; we seem full and real, and yet we are a morning mist, soon dispersed.
Thus, for my part, I have put a more interpretive spin on the title of this chapter: "The Great Mystery as Teacher". Because the Source is utter Mystery, all things are utter Mystery. This is perhaps the first lesson it has to teach us. However much we know about things, still we truly know nothing. When everything is explained, what is most fundamental still remains unexplained. In this sense all knowledge is, as Zhuangzi tells us, "peculiarly unfixed". Kierkegaard uses the image of sewing with an unknotted thread; as we sew it all unravels behind us; all well and good for our immediate purposes, but never really sewing things up.
Mystery does not tell us to abandon knowledge any more than it tells us to abandon life; it simply teaches us to live as in the constant presence of Mystery, that is, peculiarly unfixed. What we learn from Mystery in affirming it as fundamental to everything is to release ourselves into it, letting go every pretense of fixed substantiality.
Zhuangzi makes free and loose in his references to Source. He is not hung up on words, does not fear he might say the wrong thing. Too much precision may be more a sign of a false belief that something can actually be said, than careless words. (Thus is it anathema to say "One", as if "non-dual" were closer to the 'truth'.) Thus, we have "Dao", "The Great Clump", and the "Creator of Things". There is freedom here; evidence of freedom. The fish-trap has been forgotten; “who has forgotten words, that I might have some words with him?”
You can check out Scott's writings on Zhuangzi here.