What is the true state of diligent Chan practice?

When one is truly engaged in the effort of investigating Chan, because meditative concentration (samādhi) is very deep, the mind consciousness has almost nothing to occupy itself with; only the manas remains in a state of sustained examination (vicāra), deeply probing. Finally, when the causes and conditions are complete, the manas will suddenly find the tathāgatagarbha that is presently operating upon the five aggregates (pañca-skandha), and thus enlightenment is realized. At the same time, the manas transmits this message to the mind consciousness, and the mind consciousness thereupon suddenly sees the light—realizing enlightenment almost simultaneously with the manas. The manas directs the mind consciousness to slap the thigh. As long as it is the manas that has realized enlightenment, the body and mind at that moment will inevitably react differently from the ordinary state: the body and mind are tranquil and at ease (praśama), the mood is joyful and delighted, relaxed and free. If there is only the mind consciousness's understanding, there will be none of these signs and reactions, because the mind consciousness does not take charge and cannot direct the body faculty. Without meditative concentration, or if the concentration is shallow, the manas cannot be put to use, because He contacts many dharmas and cannot investigate alone, nor can He investigate together with the mind consciousness.

Generally speaking, whenever any dharma is truly realized, there is meditative concentration; the manas participates in the process of investigation, and in the end it is always the manas that realizes it and then tells the mind consciousness. If the mind consciousness realizes first and then tells the manas, the manas will be unable to fully investigate and deliberate (manasikāra), and will only reluctantly agree with the mind consciousness's views and opinions; the depth of the enlightenment is shallow, the manas does not fully and completely understand, and regression is easy. When the manas realizes it first by itself, one is often extremely firm in one's conviction and will not regress.

As for the mind consciousness alone engaging in sentimental thinking and intellectual interpretation, with the manas not participating in the entire process of thinking—even if the mind consciousness understands some principles, the manas remains muddled and full of doubts; the mind consciousness, being generally coarse, usually cannot detect the manas's mental state. Any conclusion or answer that the mind consciousness arrives at entirely on its own is neither ultimate nor thorough, lacking evidence or with insufficient evidence; there is no question of speaking of regression or non-regression, because there was never any advance in the first place—how could there be any talk of falling back?