The chapter makes the boldest epistemological claim in the book and makes it in two lines. Without going out of the door, one can know the world. Without looking out of the window, one can see the way of heaven. Then the sting: the further out one goes, the less one knows.
Taken as a claim about information it is plainly false, and it has been read as false by critics for a very long time. Nobody learns the price of grain in a distant province by sitting still. The chapter is not making that kind of claim, and the terms it uses are the evidence: what is known without leaving is the world as a whole and the way of heaven, which are patterns rather than particulars.
The argument, spelled out, is that the pattern is present wherever you happen to be standing, because it is what makes everything else the case. If returning is how the way moves, that is observable in a breath, a season or a household, and no amount of additional travel makes it more observable. Adding instances to a pattern you already have is not learning.
The second half of the chapter attaches the claim to the sage in three parallel clauses: he knows without going about, names things without seeing them, and completes without acting. The third of those brings the epistemology back into line with the book's central term, which suggests the chapter is not an isolated boast but an application of non-action to knowing.
The line about going further and knowing less remains the most quotable and the most contested sentence in it.