The original text of Tao Te Ching: "The immortal in the valley is called Xuanzang. The gate of Xuanzang is the root of heaven and earth. If it is continuous, it will not be used often. " Lao Tzu wrote the Tao Te Ching in Hangu Pass, so he called the Valley God a fairy. Valley god is not a god, but a wonderful and endless miracle. Why is it the root of heaven and earth? Because it is eternal. I prefer the beauty of women, because women are endless.
In Laozi's theory, he especially likes kindness, softness and weakness. Because only infrequent use, only lasting, only play the role of Xuanzang's heaven and earth roots, can we achieve eternity. The above is Ceng Shiqiang's explanation.