Introduction

This verse ranges a bit, though it does follow a format we see in many other verses. There is an opening position, a teaching that expands on the position, a method to realize the teaching for oneself, the ramifications for not following the method, the benefit of following the method, and a summary statement. 

At the core of this verse lies the realization that beginnings and ends contain each other. The Way and Weaving it are inseparable. Returning to the origin is simple because we have never left the origin at all.

Translation

Everything under heaven has a beginning
  that serves as its mother.

Knowing the mother,
  is knowledge of the child.
Knowing the child,
  preserves the mother.
There is no danger of it disappearing.

Block the eyes,
  shut the gates.
For the life of you,
  do not toil.

Open the eyes,
  pursue your affairs.
For the life of you,
  you’ll never be saved.

Seeing intricacies is clarity.
Protecting softness is strength.

Use the light
  to return to clarity
    no residue of personal misfortune;
This is practicing permanence. 

Commentary

Everything under heaven has a beginning
  that serves as its mother.

Knowing the mother,
  is knowledge of the child.
Knowing the child,
  preserves the mother.

What has begun, and what is the mother?

Dao and De, Great Yin and Great Yang, Cause and Effect, The Means and the End, and numerous others are all subtly different filters on one archetypal concept. Each filter has its value, and I encourage you to apply the principle to as many iterations of these relationships as possible. 

The essential notion is called “interpenetration.” Interpenetration, defined by the Oxford Learner’s Dictionary, means “the process of spreading completely through something or from one thing to another in each direction.” As an interesting example, a child’s cells can be found in the brain tissue of their mother in a phenomenon called microchimerism. The linked article concludes by saying: 

In addition to exchange between mother and fetus, there may be exchange of cells between twins in utero, and there is also the possibility that cells from an older sibling residing in the mother may find their way back across the placenta to a younger sibling during the latter’s gestation. Women may have microchimeric cells both from their mother as well as from their own pregnancies, and there is even evidence for competition between cells from grandmother and infant within the mother.

The point is to illustrate that the beginning and the end contain each other, as the seed is both the plant's beginning and the fruit's end. The Way is made by walking it, and the way we Walk reflects and generates the Way. See verse 25.

Of course, we can’t forget the pointer to the meditative experience. As the physical breath becomes Energetic Breath and Energetic Breath condenses into the Child, we return to the Mother. By caring for the child, we return to the mother (the dao), realizing that the mother has provided all the nourishment we need to know the child (see verse 20).