Introduction

The premise of this verse is very straightforward. What isn’t there is what makes something useful. 

In contemplating this text, I have found it to be equally emphasizing both “isn’t there” and “is there,” or yin/absence and yang/presence, etc polarities. To be explicit, Weaving the Virtuous Way is all about the harmonious emergence of complimentary energies from the singular pressure of the Dao. Biasing one energy over the other is nonsensical. 

Therefore, I am significantly departing from the traditional reading, which emphasizes the “isn’t there” aspect. The location of a comma added by later commentators creates this contrived emphasis.

The following translation emerges by moving that comma one character to the right. If you’d like to see the Chinese, it’s at the end of the commentary.

Translation

Thirty spokes join at one hub.
Integrating what isn’t and is,
  makes a cart useful.

In using clay to make a cup.
Integrating what isn’t and is,
  makes the cup useful.

Cutting out doors and windows.
Integrating what isn’t and is,
  makes a room useful.

Benefit from what is.
Make use of what isn’t. 

Commentary

Thirty spokes join at one hub.
Integrating what isn’t and is,
  a cart makes use of it. 

There’s no place for an axle without a hub. There’s no support for the rim without the spokes.