"Tao cannot be said. Once said, it is no more Tao."
You can understand what he means. He is saying that if you read the first statement, there is no need to go any further. "Truth cannot be said. Once said, it is no more true" -- this is his declaration. Now, if you understand, the book is finished. What can be said about the truth? Yes, it can be lived, experienced. You can love, live, be -- but definition is not possible. If you want definitions you will have to go to a university. Professors define what truth is, and each professor of philosophy defines it in his own way, and there are millions of definitions, and all are false. No definition can ever be true.
What to say about truth -- even the small experiences of life cannot be defined. What is love? Or what is the taste of sugar on your tongue? How to define it? What is beauty when you see it in a lotus flower?