The first line of the Mumonkan is:

佛語心宗爲、無門爲法門。 Buddhism makes mind its foundation and no-gate its gate.

佛 is the character for “fo,” or Buddha. And the following character, 語, means “speech,” the speech of Buddha.

But what does it mean that 佛語, translated here as “Buddhism,” makes “mind” its foundation?

Here the mind spoken of is 心, the mind (also heart) of Bodhi. It’s also called “Citta” in the Sanskrit texts. It is the “One Mind” spoken of by Master Huang-Po, because there are not two of them.

It’s precisely not the selfish, distracted, confused mind of the individual human being that’s being spoken of here, but the sky-like Mind of all the Buddhas.

宗 means school or sect. It can also mean ancestors. 爲 is “handle” or “govern.”

As for 無門, it’s “no-gate.” 門 can also mean door, entrance, opening. It can also mean “family” or “sect” or “school of thought.” 佛門 is a well known expression for “Buddha-sect” or “Buddha-gate” or “Buddha-family” which is usually translated in the West by the term “Buddhism.”

(Note the semantic overdetermination always present in Chinese texts because of the multifarious way the ideograms carry historically sedimented meaning. Sanskrit does not have this kind of polysemy.)

Then there’s 爲法門. 爲 is “to do; to make.” 法 means law, decree, or Dharma. Then we have 門, the “gate” mentioned again.

The “no-gate” doesn’t really mean that there is no gate. Mumon tells us there is a gate, and it’s the gate of no-gate. This is obviously more interesting than the simplistic logical idea than that there is or is not a gate.

The gate is the gate of no-gate. That’s the gate of the Buddhist law or Dharma. Why? Because this “no” is the pivot on which the entire Mumonkan turns, and the no-gate is the entryway to the reality of Bodhi.

But 無 does not signify a “lack of.” The No-Gate is still a Gate. It is the Gate of No-Gate.

The Zen barrier is a “Gateless Gate” (Wu-men, 無門) because it is not a barrier at all, but an open checkpoint, like a mountain valley blocked by a wisp of white cloud. It seems as if, once you step into that cloud, you will fall into the abyss and never return. Yet you have got to take the jump:

無門曰、參禪須透祖師關、妙悟要窮心路絶。 In order to master Zen, you must pass the barrier of the patriarchs. To attain this subtle realization, you must completely cut off the way of thinking. (A literal translation of the Chinese: “make poor thinking (heart) speech road”). 祖關不透心路不絶、盡是依草附木精靈。 If you do not pass the barrier, and do not cut off the way of thinking, then you will be like a ghost clinging to the bushes and weeds.

To pass the “barrier of the [Zen] patriarchs” as Mumon instructs, you must put a stop to the normal workings of your mind. For in the bold theory of T’ang Dynasty Zen, it is only a deluded “thinking consciousness” that obstructs the spontaneous realization of your innate Buddha nature.

So to cut off thinking (or “make poor thinking (heart) &c.要窮心) completely in a single instant results in the experience of 妙悟. ( 妙, mysterious, exquisite, unfathomable, 悟 understanding, realization, enlightenment).