A major issue that had long fomented in Chinese Chan and which received special attention from Jinul, was the relationship between so-called 'gradual'  漸 and 'sudden'  頓 approaches to Buddhist practice and enlightenment. Drawing upon various Chinese treatments of this topic, most importantly those established by Zongmi 宗密 (780–841) and Dahui 大慧 (1089–1163), Jinul came up with his 'sudden enlightenment followed by gradual practice'  頓悟漸修 approach to the matter of practice and enlightenment. Jinul believed that for religious practice—especially meditative practice—to have efficacy, the practitioner must have a deep and transformative experience of insight into the emptiness of things...to see their nature of innate enlightenment. If one tries to practice without such an experience, all of oneʼs practice will be based on the dualistic thinking habits that are the causes of delusion, and thus, no matter how hard one might try, no meaningful progress can be made. One metaphor that Jinul used to express this idea was that of the morning dew and the sunshine. Before the sun rises, the cool morning grass is wet with dew. Try as one may to wipe away the dew, it will continue to reappear. Once the sun rises, however, once one wipes the dew away, it is less apt to return. In the same way, once one has had an awakening experience, once efforts toward the eradication of bad cognitive and emotive habits will have enhanced efficacy.

Jinulʼs approach to Buddhist practice ended up becoming a distinctive blend of gong-an 公案 (J. kōan) meditation, coupled with scriptural study, incorporating a Hwaeom 華嚴宗 (Ch. Huayan) approach that tended to see the mutual containment of ostensive opposites. From the Chinese Chan master Dahui 大慧, Jinul incorporated the gwanhwa (觀話 'observing the key phrase of the gong-an' ) method into his practice. This form of meditation remains the main method taught in Korean Seon down to modern times. Yet on the other hand, Jinul believed that scriptural study was a vitally important component of Buddhist cultivation. This approach is shown in the fact that that Jinul did not undergo his enlightenment experiences as the result of the classical so-called personal 'mind-to-mind transmission' between teacher and student as characterized in the Seon school. Rather, each of his three enlightenment experiences came in connection with the contemplation of a passage in a Buddhist text. In his final articulation of the issue of the relationship between seon (meditative practice) and gyo (scriptural study), Jinul was influenced by the explanation of the relationship between practice and study provided by the Tang Huayan master Li Tongxuan 李通玄 (635–730). Jinulʼs philosophical resolution of this issue brought a deep and lasting impact on Korean Buddhism, and can be seen as repeated theme in the works of numerous subsequent Seon masters, including such famous figures as Gihwa 己和 (1376–1433) and Hyujeong 休靜 (1520–1604), who followed Jinulʼs way of thinking in addressing the issue of practice and study in their own writings.

Jinul produced a number of important disciples who passed on his teaching and continued to work within his discourse. His major works include: Encouragement to Practice: The Compact of the Samādhi and Prajñā Community 勸修定慧結社文 (1 fasc.), Mogujaʼs Secrets on Cultivating the Mind 牧牛子修心訣 (1 fasc.), Straight Talk on the True Mind 眞心直說 (1 fasc.), The Complete and Sudden Attainment of Buddhahood 圓頓成佛論 (1 fasc.), Resolving Doubts About Observing the Hwadu 看話決疑論 (1 fasc.), Admonitions to Beginning Students 誡初心學人文 (1 fasc.), Afterword to the Sixth Patriarchs Dharma Jewel Platform Sutra 六祖法寶壇經跋, Excerpts from the Dharma Collection and Special Practice Record 法集別行錄節要幷入私記, Essentials of the Flower Ornament Scripture 華嚴論節要 (three fascicles). Several of these have been translated by Robert Buswell in the works listed below.

References:

Buswell, Robert E., Jr. 1983. The Korean Approach to Zen: The Collected Works of Chinul. Honolulu:  University of Hawai`i Press.

----. 1986. “Chinulʼs Systemization of Chinese Meditative Techniques in Korean Sŏn Buddhism.”  In Gregory, Peter N., ed. Traditions of Meditation in Chinese Buddhism. Honolulu:  Hawai`i University Press. vol. 4 199–242. Studies in East Asian Buddhism

----. 1991. Tracing Back the Radiance: Chinulʼs Korean Way of Zen. Honolulu:  University of Hawai`i Press.

Buswell, Robert E. Jr, ed. 2012. Chinul 知訥: Selected Works. Seoul:  Jogye Order of Korean Buddhism. vol. 2 Collected Works of Korean Buddhism.

Keel, Hee-Sung. 1984. Chinul: The Founder of the Korean Sŏn tradition. Berkeley:  Center for South and Southeast Asian Studies, Univ.

Shim, Jae-Ryong. 1979. “The Philosophical Foundation of Korean Zen Buddhism: The Integration of Sŏn and Kyo by Chinul (1158–1210).” Honolulu. University of Hawai`i.