The spirit and mind of the person who has had an awakening will be at peace and immovable. It should be noted that the Chinese character jaku (寂) originally meant “without a human voice,” and nen (然) “completely of-itself-so.” Together, they connote not just peace, but also loneliness or desolation, and thus evoke a nuance of wabi. Also, the characters for fudo mean “unmoving” or “still” as well as “immovable,” and thus suggest an inward peace.
This phrase seems to come directly from the Confucian commentaries on the I Ching, one of the most ancient Chinese works extant, which has been studied in Japan from the eighth century, if not earlier:
Change is without thought. It is without fabrication. It is at peace and unmoved. When conscious, it pervades all the phenomena under Heaven. Without having reached the highest spiritual state, how can you take part in this?
Lao Tzu, in the Tao Te Ching, writes about the ungraspable:
It is quiet and tranquil, empty and at rest.
It stands on its own, and cannot be altered;
Manifests itself in all things, and is never idle.
Later, in the Huai Nan Tzu, a second-century b.c.e. work, the Tao is described as follows:
In billowing waves, it is tranquil;
When at peace, it is serene.
At peace and unmoved: this is the state in which we attain the Way.
William Scott Wilson : “The One Taste of Truth: Zen and the Art of Drinking Tea”.