In this simple exchange between Zhaozhou and a monk, there’s a question and Zhaozhou answers. Four hundred years later, Wumen’s teacher, seeing the potential of this exchange, gives Wumen the koan Mu to work with. Wumen sits non-stop with Mu for six years, in the midst of doubt, in the midst of bottomless zazen. He sweeps and sweeps and sweeps, and suddenly, the broom breaks. He hears a bell in the courtyard, and enters the realm of the ancient Zen masters. Then, a few years later, when Wumen’s students come to him asking for a method of systematically studying the mind, he writes The Gateless Gate, a book with forty-eight koans, the first one of which is Mu. In addition, there is his commentary to Mu, as clear a guideline for studying the mind as you’re likely to find. Then, there is the lineage of people who kept making Mu a deeply personal matter—transmitting the gateless gate of koan study.

“In studying Zen, one must pass the barrier set up by the ancient Zen masters.” To pass the barrier, you first have to recognize it for what it is. We must notice that there is a barrier, and recognize its full implications. We are being offered something unprecedented—on an unblemished field of perfection, buddha nature pervading all space and time—a barrier. Wumen, in the introduction to The Gateless Gate, has this poem:

Gateless is the Great Way.
   There are thousands of ways to it.
If you pass through the barrier,
   you may walk freely in the universe.

There are thousands of ways to the Great Way. There are infinite ways. That’s the problem. They are just too numerous. That’s why we’re so lost. And here comes somebody who is courageous enough and outrageous enough to say, “Mu.” What is this? Enter here.

It’s like being in an open space, like a desert stretching beyond the horizon. Amidst that vastness there is a door. Just a door. No walls or fences attached to it. Quite accessible, attractive even, but obviously a curious sight in this setting. On the door there is a sign indicating that in order for you to get to the desert, you have to enter here. The door is locked. You see this as absurd. Obviously, you can walk around the door. You can walk away. You can do cartwheels anywhere in the desert. Yet, something holds you. People have walked through that door and they claim that in that passage, on the brink of life and death you are utterly free, you can live, with great joy, a genuine life in complete freedom. You tasted that in zazen. You sense the truth. You reach for the handle.