As with many terms used in Zen and the martial arts, Immovable wisdom is often misinterpreted to have a mind that does not move, when it is almost the exact opposite; it does not stop, or is not stopped. This state is sometimes described in Japanese as Fudoshin, Immovable Mind, and many physical tests for it have been developed for Aikido (and other disciplines) examinations.
Early in their study students will misinterpret this “test” and will become hard like wood or stone…and fail. Instead they must learn not to allow their mind to be moved, or caught, by the examiner. The mind must become like still water; not “caught” by the hook as it passes through.
…the mind that does not stop at all is called Immovable Wisdom. – Takuan Soho
Takuan Soho, in a letter to the Samurai Yagyū Munenori, wrote of ”Immovable Wisdom” and how a person near enlightenment was capable of controlling a thousand arms, their mind not stopping at any particular one. He goes on to say that …one who understands this is no different from the Kannon with a thousand arms and a thousand eyes.
…the ordinary man simply believes that it is blessed because of its 1000 arms. The man of half-baked wisdom, wondering how anybody could have 1000 eyes, calls it a lie and gives in to slander. But if one understands a little better, they will have a respectful belief based on principle and will not need the simple faith of the ordinary man, or the slander of the other, and they will understand that Buddhism, with this one thing manifests its principle well.
he goes on…
All religions are like this… The ordinary man thinks only on the surface, the man who attacks… is even worse. This religion, that religion, there are various kinds but at their deepest points they are settled in the one conclusion.