Three clauses at the end of this chapter say that the way cannot be seen enough, cannot be heard enough and cannot be exhausted, and they are a compressed restatement of a passage the book has already given in full.
Chapter fourteen sets out the same three terms at length: looked at and not seen, listened to and not heard, reached for and not grasped, and it names each of the three failures. Chapter thirty-five reduces the whole apparatus to a single line and adds the fourth term, that use does not use it up.
That addition is the point of the repetition. Chapter fourteen is about the limits of perception and leaves the matter there. This chapter uses the same limits to make a claim about supply. Everything the senses can register is finite, because a thing that can be exhausted by looking is a thing with an edge, and the traveller's music and food are exactly that kind of thing. What has nothing to register has nothing to run out.
The argument only works if imperceptibility is treated as evidence rather than as an excuse, and the book is aware of the difficulty. Chapter forty-one lists the way among things that seem to be their own opposites and says plainly that the poorest sort of person laughs at it. Chapter seventy says nobody in the world understands it. The text does not pretend that an invisible, tasteless and inaudible thing is an easy proposal, and it repeatedly names the reaction it expects.
What it offers instead of evidence is the practical test in the last clause: use it, and see whether it runs out.