Thirty spokes converge upon a single hub;
It is on the hole in the center that the use of the cart hinges.
We make a vessel from a lump of clay;
It is the empty space within the vessel that makes it useful.
We make doors and windows for a room;
But it is these empty spaces that make the room livable.
Thus, while the tangible has advantages,
It is the intangible that makes it useful.
I found this passage to be somewhat cryptic, so I will offer only my interpretation.
It seems that the empty space, or the void, is the unknowable source of all existence. While we cannot perceive this ineffable emptiness, it has a direct impact on our physical beings and our daily lives.
I also have the impression that Lao Tzu is cautioning against attachment to material things. Trying to grasp and hoard things in life tends to create mental clutter and creates a barrier between ourselves and the divine essence.
Finally, I can apply this to my meditation practices. I see all the tangible things as the thoughts that clutter the mind. When I meditate, I try (often unsuccessfully) to quiet that mental chatter and open myself to the profound silence which is the subconscious mind. It is impossible for me to describe this connection. As soon as I try to analyze or think about it, the conscious mind takes over and the connection is lost. But those brief moments of deep mental quietude help put the rest of my life and thoughts into perspective.
I would love to hear your thoughts and impressions on this passage. Please feel free to share your thoughts in the comments section. Cheers!