After receiving his master's instruction, Cheng Xinzhan gained an insight: cultivation amounted to no more than two words-movement and stillness.
For him, vanquishing demons and defending the Dao beyond the mountains was movement; cultivating quietly within the mountains was stillness.
These could also be called [tension and relaxation], [labor and leisure], [work and rest], or [Civil and Martial]. At their root, they were still [Yin-Yang].
The theory of Yin-Yang stated, "Lone yang cannot give birth; solitary yin cannot grow." Applied to the two states of movement and stillness in cultivation, Cheng Xinzhan likewise gained an understanding, namely:
"Movement without stillness leads to exhaustion; stillness without movement leads to emptiness."
If one knew only movement and not stillness, one's mental strength would be exhausted. If one knew only stillness and not movement, one would sink into nothingness.
And Yin-Yang could be divided infinitely. He believed stillness could be further divided into [yin stillness] and [yang stillness].
[Yin stillness] was the fasting of the mind and entry into meditation. It was the realm described by the sage Laozi: "Reach the utmost emptiness; hold firmly to stillness. The myriad things arise together, and I watch their return." It was a state of supreme stillness in which one sat watching all things in the world turn while one's own heart remained unshaken.
[Yang stillness] was strolling leisurely through a quiet courtyard. It was the realm described by the worthy Zhuangzi: "Heaven and earth were born together with me, and the myriad things and I are one." It meant that one's heart was tranquil, yet not severed from all things in the world; instead, they influenced one another, arising together as one.
Yin and yang arose together rather than opposing each other. Cheng Xinzhan believed that when in the stillness of cultivation, one had to