In his text Encouragement to Practice: The Compact of the Samādhi and Prajñā Community (Gwonsu Jeonghye Gyeolsamun) Bojo Jinul describes the nature of the mind as numinous, sublime, and self-reliant:

In the complete insight into the true and eternal qualities of one’s own mind, if activity and stillness are interfused and the dharmadhātu is realized, then we know that the qualities of all the bhūmis, the approaches to dharma as numerous as dust motes, and the nine and ten time periods are not separate from the present thought. As the nature of the mind is numinous, sublime, and self-reliant, it contains innumerable types of dharmas. The myriads of dharmas have never been separated from the self-nature; whether they are activated or not, nature and characteristics, essence and function, and adaptability and immutability operate simultaneously and without hindrance. This mind at first is without past or present, ordinary or holy, good or evil, attachment or rejection; nevertheless, their influence is gradual. As one passes through all the stages, compassion and wisdom are gradually made complete and sentient beings are perfected; nevertheless, from beginning to end that mind does not move from one time, one thought, one dharma, or one practice.

And in his text titled Moguja’s Secrets on Cultivating the Mind (Moguja Susimgyeol), Bojo Jinul explains the experiential relationship between sudden awakening and gradual cultivation as follows:

Question: You have said that this twofold approach of sudden awakening/gradual cultivation is the track followed by thousands of saints. But if awakening is really sudden awakening, what need is there for gradual cultivation? And if cultivation means gradual cultivation, how can you speak of sudden awakening? We hope that you will expound further on these two ideas of sudden and gradual and resolve our remaining doubts. Jinul: First let us take sudden awakening. When the ordinary man is deluded, he assumes that the four great elements are his body and the false thoughts are his mind. He does not know that his own nature is the true dharma-body; he does not know that his own numinous awareness is the true Buddha. He looks for the Buddha outside his mind. While he is thus wandering aimlessly, the entrance to the road might by chance be pointed out by a wise advisor. If in one thought he then follows back the light [of his mind to its source] and sees his own original nature, he will discover that the ground of this nature is innately free of defilement, and that he himself is originally endowed with the non-outflow wisdom-nature which is not a hair’s breadth different from that of all the Buddhas. Hence it is called sudden awakening. Next let us consider gradual cultivation. Although he has awakened to the fact that his original nature is no different from that of the Buddhas, the beginningless habit-energies are extremely difficult to remove suddenly; and so he must continue to cultivate while relying on this awakening. Through this gradual permeation, his endeavors reach completion. He constantly nurtures the sacred embryo, and after a long time he becomes a saint. Hence it is called gradual cultivation. This process can be compared to the maturation of a child. From the day of its birth, a baby is endowed with all the sense organs just like everyone else, but its strength is not yet fully developed. It is only after many months and years that it will finally become an adult.

But the sudden breakthrough wherein a practitioner awakens to the nature of his or her mind isn’t dependent upon any expedients or gradual methods. Since we have never been apart from this nature, and cannot be separated from it, there are no temporal stages to recognizing the nature of awareness. Just as a person cannot literally jump out of their skin, similarly we can’t be separated from this intrinsic awareness which is imbedded in every experience. But due to chasing after externals, this effortless awareness is not realized. Jinul continues:

Question: Through what expedients is it possible to trace back the radiance of one’s sense-faculties in one thought and awaken to the self-nature? Jinul: The self-nature is just your own mind. What other expedients do you need? If you ask for expedients to seek understanding, you are like a person who, because he does not see his own eyes, assumes that he has no eyes and decides to find some way to see. But since he does have eyes, how else is he supposed to see? If he realizes that in fact he has never lost his eyes, this is the same as seeing his eyes, and no longer would he waste his time trying to find a way to see. How then could he have any thoughts that he could not see? Your own numinous awareness is exactly the same. Since this awareness is your own mind, how else are you going to understand? If you seek some other way to understand, you will never understand. Simply by knowing that there is no other way to understand, you are seeing the nature. Question: When the superior man hears dharma, he understands easily. Average and inferior men, however, are not without doubt and confusion. Could you describe some expedients so that the deluded too can enter into enlightenment? Jinul: The path is not related to knowing or not knowing. You should get rid of the mind which clings to its delusion and looks forward to enlightenment, and listen to me. Since all dharmas are like dreams or phantoms, deluded thoughts are originally calm and the sense-spheres are originally void. At the point where all dharmas are void, the numinous awareness is not obscured. That is to say, this mind of void and calm, numinous awareness is your original face. It is also the dharma-seal transmitted without a break by all the Buddhas of the three time periods, the successive generations of patriarchs, and the wise advisors of this world. If you awaken to this mind, then this is truly what is called not following the rungs of a ladder: you climb straight to the stage of Buddhahood, and each step transcends the triple world. Returning home, your doubts will be instantly resolved and you will become the teacher of men and gods. Endowed with compassion and wisdom and complete in the twofold benefit, you will be worthy of receiving the offerings of men and gods.

The important distinction is between recognizing this empty, numinous awareness or not recognizing this awareness. This awareness itself is always effortlessly present, hence the designation “always-present awareness” (changzhi). Recognizing this is called “sudden awakening.” Not recognizing it is called “delusion.”

But even after recognition there is a need to consistently cultivate this recognition — returning to this effortless awareness again and again. This is because habitual tendencies have not yet been eliminated, and passion, aggression, and delusion will recur as habitual patterns to infect our bodily conduct, speech, and thoughts whenever there is a lapse in mindfulness and our original face is forgotten.

This is where the unique Chan approach of observing the huatou (Korean: hwadu) is so helpful in directly seeing through habitual patterns of conflicted emotions and egocentric thoughts and remaining dedicated to the non-constructed simplicity of awareness itself. In this way we can gradually cultivate complete devotion to awakening in every moment. We can cast off frivolous, worldly concerns and fully embody both compassion and wisdom. We can devote our entire life to this uninterrupted realization of the dharmadhātu.

Quotations from Buswell Jr., Robert E. The Korean Approach to Zen: The Collected Works of Chinul. University of Hawaii Press, 1983.