Look, and it can't be seen.
Listen, and it can't be heard.
Reach, and it can't be grasped.
Not as a separate entity, anyway...
Above, it isn't bright.
Below, it isn't dark.
it returns to the realm of nothing.
Form that includes all forms,
image without an image,
subtle, beyond all conception.
It can't be conceived of, as it is beyond the realm of ideas. The first two lines sound like a specific dismissal that Tao is the earth itself. When the sun is up, the earth is bright above, and it's always dark if you dig deep into the earth. The realm of nothing is where all things have their beginning. A friend of mine calls nothing the "infinite potentiality." It's not an image itself, because it contains all images.
Approach it and there is no beginning;
follow it and there is no end.
You can't know it, but you can be it,
at ease in your own life.
Just realize where you come from:
this is the essence of wisdom.
The first two lines sound a lot like learning taiji. Parts of it seemed infinitely familiar to me, hence "no beginning." Other parts, I will continue to work on for my whole life, and perhaps beyond, hence "no end". Knowing the form in the mind is worthless unless the body also knows it; then you can become the form.