Seongcheol (April 6, 1912 – November 4, 1993) is the dharma name of a Korean Seon (Zen) Master. He was a key figure in modern Korean Buddhism, being responsible for significant changes to it from the 1950s to 1990s.
Seongcheol was widely recognized in Korea as having been a living Buddha, due to his extremely ascetic lifestyle, the duration and manner of his meditation training, his central role in reforming Korean Buddhism in the post-World War II era, and the quality of his oral and written teachings.[1]
Seongcheol also set a clear benchmark that the practitioner could apply to gauge his level of practice. Throughout his life, many followers came to him to obtain acknowledgement of their enlightenment. He was dismayed at the number of people who thought they had attained perfect enlightenment by experiencing some mental phenomenon during their practice.
He therefore reiterated that every enlightened person from the Buddha and on had asserted the same definition of what enlightenment is. True attainment, he quoted, came only after going beyond the level of being able to meditate in deep sleep. Only after being able to meditate on a gong'an
(jap. koan) continuously, without interruption, throughout the waking state, then the dreaming state, and finally in deep sleep, one reaches the state where enlightenment can become possible.
Before any of this, one should never claim to have become enlightened, even though there may be many instances of weird mental phenomena that happens during one's practice. The levels he identified were:
In the waking state, one mind: the state where the practitioner can meditate on a gong'an continuously throughout the day without interruption, even through talking and thinking.
In the dreaming state, one mind : the state where the practitioner can meditate on a gong'an continuously in the dreaming state.
In deep sleep, one mind): the state described above, where the practitioner can meditate on a gong'an continuously through even the deepest sleep.
In death, attain life: from the previous state where all thoughts are overtaken by the gong'an (therefore, the practitioner is considered mentally "dead"), the moment of attaining enlightenment, that is, "life."
Great, round, mirror-like wisdom: the state of perfect enlightenment, using the analogy of the bright mirror for the great internal wisdom that comes forth during enlightenment. The final state where the practitioner loses the sense of self, is liberated from his karma, and therefore, all future rebirths.
http://en.wikipedia.org/wiki/Seongcheol