The bodhisattva Avalokiteshvara-the one known in Chinese as Kwan Yin-describes Mu this way in the Heart Sutra, probably the most important sutra in Zen:
In emptiness there is no form, no feelings, perceptions, impulses, consciousness. No eyes, no ears, no nose, no tongue, no body, no mind; no realm of eyes and so forth until no realm of mind cosciousness. No ignorance and also no extinction of it, and so forth until no old age and death and also no extinction of them. No suffering, no origination, no stopping, no path, no cognition, also no attainment with nothing to attain.
... Even if this emptiness looks a lot like death or like the world coming to an end. It's effect on our lives is astonishing. It can free you from every fear. There's no memory, habit, or buried trauma-no obstacle of any kind-that it can't dissolve like water wearing down a stone.
... The nature of things doesn't change at all. What has changed is our perception of them. We discover that everything is Mu, and that Mu is everything."Form is emptiness," and "Emptiness is form." And when we see our obstacles for what they are-fundamentally nothingness-their hold over us gradually erodes
The Book of Mu (P.278-9)