Tao Te Ching, 6

The spirit of the valley never dies. It is called the subtle and profound female. 

The gate of the subtle and profound female Is the root of Heaven and Earth. 

It is continuous, and seems to be always existing. Use it and you will never wear it out. (Tao Te Ching, 6)

Today, I would try to interpret the above text which is translated by Wing-Tsit Chan.

It can be understood from the above text that Lao Tzu is advocating non-violence which is only done when one is not so much into humanity. Lao Tzu is more on knowing the natural way of things which is usually calm and tranquil. He described the Tao as a "she", a female because usually during wars, females are not into battlefields. They stay at home and watch over children. She calms the house and she is also the one who gives birth. Using a female as a metaphor for the Tao, it can be understood that the Tao is really against wars or any violence. As a female is into  peace, so as the Tao.

The Tao is the root of Heaven and Earth because naturally, these two are also of calmness and tranquility. They are continuous. Because of their silent characteristic, they seem to be invisible but people cannot deny their existence.  They are always there yet sometimes, they are not recognized. When one will use them it will not wear out because the Tao is eternal. It will never be exhausted because it is the beginning of all things.