The Tao that can be spoken is not the eternal Tao
Thus, constantly free of desire
These two emerge together but differ in name
The Tao that can be completely explained or expressed in words is not the constant, eternally unchanging and true Tao.
If the name of this Tao can be defined with words, then it is not the constant, eternally unchanging name of the true Tao.
Names did not exist prior to Creation. The nameless Tao is therefore the source of the universe.
Once it manifests itself as the physical universe, it can be named. Everything is derived from it through natural processes. It is therefore the mother of all things.
If we approach the Tao without self-serving desires, we can readily observe its inner wonders and marvels. This establishes a direct connection with the source, the vast intelligence of universal consciousness. This gives us flashes of powerful, intuitive insights, as well as free-flowing creativity.
If we approach the Tao full of self-serving desires, then we can only observe its external physical manifestations, rather than its inner essence. These desires block the connection and interfere with the Tao process. We often do this to ourselves.
The Tao's external manifestations (life, nature, the cosmos, and so on) and its inner wonders (oneness, the living void, the flow, etc.) are both properties of the ultimate reality. Although we call them by different names, they are but two sides of the same coin.
This unity of these two aspects gives us an interesting paradox. They seem distinctively different, and yet they lead to one another. Understanding of the Tao's inner essence gives us greater understanding of its outer manifestations, and vice versa.
Our recognition and acknowledgement of this paradox will open the door for us to further explore the infinite wonders of the Tao.
The "Nameless Name" - that which existed before there was anything to name - is a synonym for the Tao.
The main idea here is that the Tao is a concept beyond reason and logic. It is the universal principle that permeates every action and every phenomenon, but it cannot be adequately understood through the rational mind. To comprehend it completely, you must exercise your intuition and get in touch with the fundamental divinity that connects everyone.
Lao Tzu is also pointing out the limitation of spoken words and written texts. Our tendencies to categorize, define and analyze only give us the limited understanding of how the Tao acts upon the material world. This is exactly what happens when we study physics, biology, chemistry, and other natural sciences.
On the other hand, if we free ourselves of this limiting human desire to put everything into words, and become aware of our wordless communion with nature, we can catch glimpses of a divine wisdom. Beyond categories, definitions, and analyses, it is wisdom far more profound than anything that academic knowledge, science and technology can offer.
One translation renders the first line as "The way that can be trodden," which fails to take the above into account. Another translation mistakes "can" as "possible" and waxes poetic about "The possible Tao." That's even further away from the original meaning.
In this context, this character means "ever-lasting." In one instance a translator renders it as "absolute," which is close, but not quite correct.
There are many other erroneous translations of the first line, such as the following:
The Way that can be experienced
They are erroneous because the second Dao, when used as a verb, can only means to talk, to speak, etc. It can never mean to follow or to experience. Not in modern or ancient Chinese, and not in any conceivable context. Such mistakes were fairly common in the past, when Western scholars' understanding of Chinese was still in its infancy.