The mind and body have an absolute ruler, and that is principle (li); ching, ch’i, and spirit have an absolute ruler, and that is sincerity.
Sincerity is the way of heaven, and he who is sincere follows the way of humanity. Both of these are inextricably bound up with consciousness. If you understand the principle of the unity of heaven and humanity, you will naturally absorb the circulating ch’i of sun and moon. This ch’i is the circulation of consciousness, for spirit is naturally concealed within principle. Finally, we can speak of the martial and the spiritual, sagehood and immortality. If one speaks of the body and mind from the point of view of martial arts and applies these principles to the cultivation of power, it must be in the context of the essence of tao. It is a mistake to focus exclusively on physical skills.
from Lost T’ai-chi Classics from the Late Ch’ing Dynasty, by Douglas Wile
Sincerity? What does that have to do with martial arts?
“…ching, ch’i, and spirit have an absolute ruler, and that is sincerity. Sincerity is the way of heaven…” It’s not the first thing that comes to mind when thinking about martial arts, but here it is in the Yang Family Forty Chapters…the absolute ruler of the insubstantial qualities that characterize the internal arts: jing, qi, and shen

William C. C. Chen
Most of our focus in our gongfu goes naturally to the principles: “absolute ruler” of mind and body.
A principle is “a fundamental quality or attribute determining the nature of something; an essence.” The principles of a particular martial art are what characterize it as its own thing.
Taijiquan, for example, emphasizes softness, song, root, and expressing energy through a whole-body energetic connection (coherence).
Sincerity means honest, true, and real. Authentic. It’s more than just “accurate.” Or “correct.” There is a heartfelt quality to it: a sincere person cares that their words and actions ARE as they appear.
Sincerity demands participation. “Sincerity is the way of heaven,” but that is not enough. “He who is sincere follows the way of humanity,” too. The magic happens when we bring that sincerity into alignment with the principles. “Both of these are inextricably bound up with consciousness.” When we bring that participatory consciousness to our practice (to our lives), “you will naturally absorb the circulating ch’i of sun and moon.”
How cool is that! To paraphrase: When you meet your gongfu with your whole being, authentically and sincerely, the spirit that is concealed in the principles will become apparent and you will access the power and energy of the Big Qi (the circulating qi of sun and moon).
At that point, “we can speak of the martial and the spiritual, sagehood and immortality.” We have moved far beyond physical skills. We are “cleansing the doors of perception,” as Blake might say. (“If the doors of perception were cleansed every thing would appear to man as it is, Infinite. For man has closed himself up, till he sees all things thro’ narrow chinks of his cavern.”)
Sincerity goes far beyond, “I try to do my form correctly, as taught by my teacher.” If the teacher is good, then you may have learned the principles well. But that only gets you as far as mind and body. Jing, qi, and shen require more. You must MEET the activity, the moment, the space with your whole being. You must be able to get out of the story…including the story that says “this is the correct form.”
When you are sincere in your gongfu, you are not concerned with appearances. They will take care of themselves. You want to FEEL the principles, not just SHOW them.
It is in the MEETING where principle and sincerity come together.