The three gates discipline consisted of a curriculum of Buddhist practices in the late Joseon Dynasty. Research on the subject is scarce, however. The discipline arose from Bojo-jineul(普照知訥, 1158~1210)'s idea of the three gates: Seongjeokdeungjimun(惺寂等持門: the gate of equal maintenance of serenity and alertness), Wondonsinhaemun(圓頓信解門: the gate of belief and understanding of perfection and epiphany), and Gyeongjeolmun(徑截門: the gate of direct cut). The idea of three gates resulted from Jineul’s enlightenment and formed the basis of study for students. It adhered to the ideals set forth by Jeonghyegyeolsa(定慧結社: an association of meditation and wisdom) by establishing Wondonsinhaemun and Gyeongjeolmun based on Seongjeokdeungjimun. The idea was changed drastically during the late Koryo Dynasty period. Taego-bou(太古普愚, 1301∼1382) and Naong-hyekeun(懶翁惠勤, 1320~1376) selected only Gyeongjeolmun of Khanwhaseon(看話禪: Koan Meditation) to the exclusion of Seongjeokdeungjimun and Wondonsinhaemun. It was what is called ‘the Khanwhaseon Absolutism.’
As the Confucian disposition of the Joseon Dynasty replaced the Buddhist Koryo Dynasty, Buddhism was also changed drastically. At that time, around ten Buddhist sects were combined into the sect of Zen and doctrinal studies(禪敎兩宗). Therefore, Zen Masters could no more adhere to Gyeongjeolmun. In compliance with the integration of sects by the government, the Zen school(禪宗) tolerated doctrinal studies(敎學) and the pure land belief(淨土信仰). Thus the idea of combining the Zen school with doctrinal studies and the Zen school with the pure land belief gradually became common. Namely, Zen masters began to embrace doctrinal studies as one of the theories of Zen and to admit the theory of the western pure land(西方淨土). Eventually, Heoeun-bou(虛應普雨, 1505∼1565), who had revived Buddhism during the reign of King Myeongjong, established the foundation for the three gates discipline in the late Joseon Dynasty through the theory of unity of Confucianism, Buddhism and Daoism as well as of Zen, doctrinal studies and the pure land belief.
Cheongheo-hyujeong(淸虛休靜, 1520~1604), who is believed to have taken the course of Buddhism in the late Joseon Dynasty, suggested Chamseonmun(參禪門: the gate of Zen meditation) and Yeombulmun(念佛門: the gate of chanting Buddha) as a method of practice to students. He said that a person who studies in the context of Chamseonmun must pursue a living phrase(活句) of Gyeongjeolmun, not a dead phrase(死句) of Wondonmun(圓頓門: the gate of perfection and epiphany). In addition, he mentioned the pure land in the mind(唯心淨土) and the western pure land simultaneously and encouraged chanting. Finally, the three gates discipline, which had been forgotten since Jineul’s time, was revived. However, since Wondonmun was defined as a dead phrase, Hyujeong’s theory actually consisted of Gyeongjeolmun and Yeombulmun.
Hyujeong’s disciple Pyeonnyang-eongi(鞭羊彦機, 1581~1644) suggested a detailed explanation of the three gates discipline for the first time. So, in the true sense, the three gates discipline in the late Joseon Dynasty arose from Eongi. He established a curriculum of the discipline which consisted of Gyeongjeolmun, Wondonmun, and Yeombulmun. According to Eongi, Gyeongjeolmun focuses on scriptures of the Patriarch(祖師), Wondonmun is concerned with Avataṃsaka(華嚴), and Yeombulmun chants Amita-Buddha in the mind(自性彌陀). Though Wondonmun and Yeombulmun were both courses of Zen practice, Wondonmun admitted the study of the Avataṃsaka Sūtra(華嚴學) while Yeombulmun admitted the theory of the western pure land. Eventually, Gyeongjeolmun of the Zen sect embraced doctrinal studies and chanting Buddha when the sect of Zen and doctrinal studies transformed into the Zen sect during the late Joseon Dynasty period.
In the late 17th century, an academic argument concerning Taekeuk(太極論爭) arose in the Confucian community and another argument concerning the nature of the mind(心性論爭) arose in the Buddhist community. These arguments were very similar to each other in many aspects. When one consider these similarities, an ideological interaction between Confucianism and Buddhism becomes possible. There is no evidence which supports this assumption; however, it is not very hard to find a case of intellectual relationships between thinkers from both communities. Thus there is a possibility that the Buddhist argument was influenced by the other one in the Confucian community. And the academic trend could have encouraged Buddhists to systemize an education course for monks and to develop a passion for academics.
In the 18th century, the publication of Buddhist books by Baegam-seongchong(栢庵性聰, 1631~1700) revived the study of the Avataṃsaka Sūtra. In 1681, a Chinese ship shored up on the coast of Imja Island in South Jeolla Province, and some of Buddhist books from the wrecked ship were gathered by Baegam-seongchong. He published some of the books, and among these published books were Hwaeomsocho(華嚴疏鈔) and Gisinnonsopilsakgi(起信論疎筆削記). Hwaeomsocho, which was originally written by Cheongnyang-jinggwan(淸凉澄觀, 738~838), and had been missing since the early Joseon Dynasty. The re-publication of this book by Baegam-seongchong reawakened the study of the Avataṃsaka Sūtra in the 18th century. Buddhist temples all around the country were filled with monks who read Avataṃsaka Sūtra and many famous Zen masters lectured on the Sūtra. Massive Buddhist ceremonies of the Avataṃsaka Sūtra were occasionally held and, sometimes, more than a thousand people attended the ceremony. The re-popularization of the study of the Avataṃsaka Sūtra enabled people to have better understandings of Wondonmun. Thus Wondonmun came to have the same authority with Gyeongjeolmun, and it was not a part of Zen study any more. Wondonmun became a part of doctrinal study and Wondonmun itself meant the study of the Avataṃsaka Sūtra at the time.
Meanwhile, in the 18th century, the practice of chanting Buddha was also reawakened. Since the early Joseon Dynasty period, Zen masters had not denied the theory of the western pure land and chanting Buddha was recommended by them. It was the most useful method of Buddhist practice for people at the time. The publication of Yeombulbogwonmun(念佛普勸文) played the most important role in the popularization of chanting Buddha. The book encouraged the pure land belief and chanting Buddha. The wooden blocks of the book were engraved a total of 8 times during 80 years since it was published for the first time in 1704.
The fact that chanting Buddha was popularized in the 18th can also be proven by historical records about Yeombulgyeolsa(念佛結社: an association of chanting Buddha) and Yeombulgasa(念佛歌詞: a lyric of chanting Buddha). There were many Buddhist associations in the late Joseon Dynasty period. Most popular among those associations was Yeombulgyeolsa. It was organized in Buddhist temples around the country with the name of ‘Yeombulgye(念佛契)’, ‘Manilhoe(萬日會: The term "manilhoe" derives from a particular Buddhist practice, in which a name of Buddha is chanted for ten thousand days. "Manil" translates literally to "ten thousand days")’, etc. According to related historical records, there were 3 associations organized in the 18th and 19 associations in the 19th, however, there must have been much more than that. In the 19th century, the Manilhoe in Keonbongsa Temple(乾鳳寺) triggered nationwide popularization of Yeombulgyeolsa. The Manilhoe in Keonbongsa Temple was so successful that it was held 5 more times in the 19th and the temple was known as the sacred place of Manilhoe. Meanwhile, most Yeombulgasa were passed down through the generations by word of mouth and the analysis of Yeombulgasa shows us that it encouraged one to rebirth in the western pure land by chanting Buddha. Since Yeombulgasa assumed the form of literature, it was easy for people to understand. So it is possible to see that Yeombulgasa played an important role in the popularization of Chanting Buddha.
Because of the popularization of the study of Avataṃsaka Sūtra and chanting Buddha, the three gates came to mean a gate of practice. In the late 18th century, Jinheo-palgwan(振虛捌關, ?) clarified in his book Sammunjikji(三門直指), that there was only an order of the three gates, not superiority and inferiority among those gates. Kiseong-kueseon(箕城快善, 1693~1764) who was the author of Cheongtaeckbeopboeunmun(請擇法報恩文) said that Yeombulmun was the most superior gate of practice. When one consider the fact that the memorial tablets of 12 Zen masters(宗師) and 12 Sūtra masters(經師) were treated without discrimination in Daeheungsa Temple(大興寺) in 19th century, it is possible to see that those three gates were of equivalent importance.
A group of Zen masters who were dissatisfied with the equality of the three gates tried to prove the superiority of Gyeongjeolmun. Beakpa-geungseon(白坡亘璇, 1767~1852) ranked Josaseon(祖師禪: Ancestry Zen), Yeoraeseon(如來禪: Tathagata Zen), and Uiriseon(義理禪: Semantic Zen) in order and insisted Josaseon was superior than the others. The Josaseon means Gyeongjeolmun. Choui-uisun(草衣意恂, 1786~1866) criticized Geungseon’s classification of Zen; he insisted that Zen could be divided into Gaegoeseon(格外禪: Exceptional Zen) and Uiriseon by Dharma(法) while it also could be divided into Zen into Josaseon and Yeoraeseon by humanity(人). Uisun thought Josaseon was identical with Gaegoeseon and Yeoraeseon with Uiriseon. Thus he did not admit superiority and inferiority of Zen. This argument concerning Zen was derived from an argument concerning the three gates discipline. The point of the Zen argument was how to identify Uiriseon since Uiriseon contains context of Wondonmun and Yeombulmun in it. Thus the argument was derived from the different understandings on Gyeongjeolmun, Wondonmun and Yeombulmun.
The fact that the Zen argument was concerned about the context of the three gates discipline shows us that the discipline was well known in the 19th century. Seoldu-yuhyeong(雪竇有炯, 1824~1889), for example, suggested the three gates for Buddhist practice in his book Sansayakcho(山史略抄) in the late 19th. Geummyeong-bojeong(錦溟寶鼎, 1861~1930) also recommended the three gates as a representative basis of Buddhist practice.
From the information gathered above, it is possible to see that the three gates were in complementary connection. Buddhist students must have studied Zen of Gyeongjeolmun or the study of Avataṃsaka Sūtra of Wondonmun according to their needs. They also probably enlightened people and themselves by chanting Buddha. The three gates discipline must have been considered as the way of enlightenment and have been popularized among people in the late Joseon Dynasty.