If one can't speak about the Tao or know about it, what is one speaking of? It seems like like trying to capture a mirage in one's hands. — Manuel

This is my understanding. Other's disagree.

You're exactly right. The opening lines of the Tao Te Ching are:

The Tao that can be spoken is not the eternal Tao
The name that can be named is not the eternal name

So, the book is words about something that can't be put into words. Lao Tzu recognized the irony. What I believe is that Lao Tzu's purpose is to help us experience something that comes before words, the Tao. The focus should be on the experience, not the meaning of the words. As I said, others on the thread disagree with me.