The chapter is built on a single argument that it states twice with the terms reversed, and the doubling is what makes the point.
The great way floods out to left and right. The ten thousand things depend on it to be born and it refuses none. When the work is done it claims no title. Because it clothes and feeds them without lording it over them, it may be named among the small. Because they all return to it and it still does not lord it over them, it may be named great.
The same behaviour therefore earns two opposite descriptions, and the chapter offers no way to choose between them. Not asserting itself makes the way small when you look at how it behaves, and great when you look at what depends on it, and both are correct because greatness here is not a property of the thing but of the relation others have to it.
That is why the closing line follows. Because it never makes itself great, it is able to accomplish greatness. The sentence is often quoted as a piece of advice about modesty, and it is closer to a definition: greatness that has to be asserted is a claim about oneself, and a claim about oneself is exactly the thing that turns others into an audience rather than into dependants.
The image at the head of the chapter, of water spreading out to both sides, is one of the book's many uses of flood and river. What distinguishes this one is that the water is not going anywhere in particular. It is described as overflowing without direction, which is the figure for something that meets everything and selects nothing.