The koan itself is succinct, Zhaozhou’s response to the monastic’s question as brief as it can be. Then Wumen begins the commentary with this line: “In studying Zen, one must pass the barriers set up by the ancient Zen Masters.” He directly links this particular dialogue with a systematic approach to spiritual practice that is made available through koan study, a thirteen-hundred-year-old deliberate method of verifying the truth that requires that we embody and penetrate the barriers that were created by those who dedicated their lives to the search for clarity and to helping others.

When Daido Roshi introduced this koan into my practice, it felt like a lifeline had been thrown to me. I knew that I had to grab on to it with all my might. I recognized that something with tremendous power and possibility was being offered to me, and it was only then, when I began engaging Mu, that I realized that I had been drowning amidst my life. I realized how, in spite of the years I had already spent sitting and studying my mind, I was still a ghost clinging to bushes, mesmerized by appearances.

 

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In taking up Mu, I was asked to respond to a specific question and give a specific response. There was no room for me to wiggle around. There was no room for sophistry, intellectualizations, justifications, emotional storms. Mu was pure, simple and direct. It was—and remains—life-saving. Mu will bring somebody out of the pit of despair. It will also counter the possibilities of us indulging in grandiosity, or of investing ourselves in some special, fleeting occasions of insight. Mu is real. It’s unequivocal. It is a barrier that we must pass through, to assure ourselves that we can be free.

In some Zen lineages, the first talk of every sesshin is on Mu. In a few Korean schools of Zen, Mu is the only koan you do for your whole life of practice. You pass Mu repeatedly, deepening your relationship to the glimpse of sanity and its infinite possibilities. In our lineage, we begin with Mu, and come back to it at the end of our formal koan training, using the Five Ranks of Master Dongshan to appreciate the various facets of Mu. We keep returning to the barrier, recognizing the clarity of the original glimpse that just keeps on opening and affecting everything about our lives. Mu is utter simplicity and infinite complexity.