道沖而用之或不盈。
淵兮似萬物之宗。
挫其銳，解其紛，和其光，同其塵。湛兮似或存。
吾不知誰之子，象帝之先。
The Tao is empty, and it can never be used up or be filled.
It is so deep as if it were the origin of all things!
It rounds off its sharpness, unties the tangles; softens its light, and merges with the dust. It seems to be absent, yet it is present always.
I do not know whose child it is. It appears before the ancestor of all.
Lao Tzu continues to explain what Tao is. The Tao to him is emptiness, void, hollowness, vacuity, vacancy, blankness, abyss, bareness…but also limitless and bottomless, so it can not be filled. It is so vast that everything arises from it, so that it seems to be the origin of all.
Here he also describes how Tao appears in our life – rounds off its sharpness, unties the tangles; softens its light, and merges with the dust.
Bear all of the above in mind and do not forget that Tao is all about hollowness and emptiness as you read the continuation of this in chapter 16 – To empty yourself totally and attain the peace in your heart. (致虚极，守静笃)
In other words, the utmost state for Tao is not only to understand the emptiness but to become emptiness (thoughtlessness), thereby Tao, and become one.
