Wumen Huihai said:

 

Isn’t there a person who will penetrate the barrier gate of the patriarchs? With the three hundred and sixty bones of the body and the eighty-four thousand pores, the entire body must give rise to the ball of doubt. In investigating the character mu, one must take this character mu up day and night, all the time. Do not understand it in the sense of “it is empty”; do not understand it even through the sense of “is” or “is not.” Just like a molten lump of metal, it will not come out no matter how much one tries to spit it out. In this way one must get wholly rid of that mistaken cleverness one had until now. Continue steadily in this way, and if one’s study matures, then automatically the body and the mind will become a single lump together with the character mu and one will form them into one piece. This is just like a deaf-mute who, although he dreams, still only knows of it himself, and cannot tell it to anybody.

 

And so suddenly if the hwadu is broken, a vigor that shakes heaven and earth is produced. This is just as if one snatched the great sword away from General Guan Yu (the god of war), picked it up in one’s hand, and so if you met the Buddha you killed the Buddha, and if you met a patriarch you killed the patriarch. And even on the hill of birth and death you gain a great freedom, and even in the life of a sentient being you can enjoy the samadhi of play.

(Wumen’ guan case 1)

 

In order to directly enter into hwadu one must certainly give rise to doubt. If one takes up a hwadu, one asks, “Why is it said that a dog has no Buddha-nature?” and “Why is it said the Buddha-dharma is a dried shit stick?” One must earnestly enter into doubt. One does not doubt with one’s head, one must doubt with the whole body. Therefore Seon Master Wumen Huikai said that doubt is “with the three hundred and sixty bones of the body and the eighty-four thousand pores, one must use all the body.”

 

If one tries to make an extreme and earnest doubt by giving rise to doubt in the hwadu, at any moment, while that doubt persists, that is called the feeling of doubt (uijeong). If we speak simply of what the feeling of doubt is, it means the state of doubt that naturally occurs when one purely doubts the hwadu. It is not consciously doubting as much as one can, but is the maintaining of the doubt like a kind of feeling.

 

If one takes up the feeling of doubt in this way, even if one does not forcibly doubt the hwadu, one will automatically be immersed inside the hwadu. Even if one does not doubt, naturally one will come to doubt, and even if one does not take up the hwadu, naturally one will be obsessed by the hwadu. And therefore Seon Master Mengshan Deyi said, “If the doubt deepens, even if one does not take up the hwadu, naturally the hwadu will appear.”

 

If one tries to enter earnestly into doubt about the hwadu, the feeling of doubt conglomerates into a lump and that is called the ball of doubt (uidan). The doubt that is wound round and round and massed together is the ball of doubt. Therefore, later this ball of doubt is revealed alone. That is called “the ball of doubt alone on the road” (uidan doglo). If that ball of doubt is alone on the road, the hwadu and I become one, and we make a body that cannot be divided one from the other. The mass of doubt becomes a ball of flames and it is a condition wherein there are no gaps into which other things can intervene. This condition is called “formed into one piece” (taseong ilpyeon). The hwadu clearly has become one piece. If it is formed into one piece, the habits of unintentionally pondering, calculating and comparing are left behind, and one merges into one with the many and varied things.

 

Seon Master Huangbo took up the hwadu of the character mu and fiercely investigated it, saying, “If one sees the days and months go by, at any moment one may become one piece, and if suddenly the flower of the mind blooms, one will be enlightened to the sphere of the Buddha and the patriarchs.” Just as if when a plum blossom gives off a fragrance, this means it has tolerated the depths of winter. Seon Master sung of that season as follows:

 

 

Although the practice of the hwadu thus displays the concrete process of shifting from the stage of the feeling of doubt to the ball of doubt, and then that forms one piece, there are also occasions when, according to the recorded sayings, the feeling of doubt, the ball of doubt and the formation into one piece are written of as the same concept.

 

If the feeling of doubt matures, then it becomes like a silver mountain and iron walls, where all the exits of thinking are intercepted. Seon Master Boshan emphasized that only when one had smashed the silver mountain and iron walls could one go on to be enlightened.

 

Silver mountains and iron walls indicate a realm that is solid, hard and precipitous, and difficult bore through or leap over. This means an acute condition where there is no opposite shore, and is inescapable, not to the left or right, front or back, and the feeling of doubt is pure. Silver mountains and iron walls means an iron wall made of silver whose thickness cannot be known. This iron wall obstructs in all directions, left and right, front and back. Therefore one cannot advance or retreat even a step. Likewise, only if one can bore through and get out will the brilliant news come for the first time.