Having read numerous books on philosophy and religion, both and Eastern, he reportedly felt dissatisfied, being convinced that these could not lead him to truth. One day, a Seon monk gave Seongcheol a copy of ''The Song of Attainment of the Tao'' , a Seon text written by Young Ga Hyun Gak in the Tang dynasty. Seongcheol felt as if "a bright light had suddenly been lit in complete darkness," and that he had finally found the way to the ultimate truth.
Ten years as a hermit in Seong Juhn Am
In 1955, Seongcheol was appointed as the patriarch of Haeinsa, but disappointed by the direction that the reformation was taking, Seongcheol declined, removing himself from the forefront and moved to a hermitage near Pagyesa in the Palgong mountains near Daegu to deepen the meditative and enlightened stage that he had attained. The hermitage was named Seong Juhn Am and it was here that Seongcheol began to build the scholarly foundations that would later support his spiritual teachings. Seongcheol surrounded the hermitage with barbed wire so as to keep outsiders out and himself within its boundaries. Never leaving the boundaries of the small hermitage for an incredible ten years, he deepened his meditation and studied the ancient Buddhist canons, Zen texts, sutras, modern mathematics, physics, chemistry, biology, and even taught himself English so as to keep current on international affairs. This decade of self-education would affect his future teachings significantly. Whereas Jinul had initially asserted that with enlightenment comes the need to further one's practice by gradually destroying the karmic vestiges attained through millions of rebirths, Huineng and Seongcheol maintained that with perfect enlightenment, all karmic remnants disappear and one becomes a Buddha immediately.
He also expounded on the true definition of the Middle Way , stating that it was not limited to avoiding the two extremes of sensual indulgence and self-mortification as many understood, but that it was also an explanation of the state of nirvana where all dualities fuse and cease to exist as separate entities, where good and bad, self and non-self become meaningless. He compared this to the common misconception that had ruled pre-Einsteinian physics, that energy and mass were two separate entities, but which Einstein had elucidated as interchangeable dual forms with the relationship described by ''E=mc?'', thereby proving the equivalence of one to the other. He also compared this to the fusion of space and time into spacetime, and also formed the analogy of ice and water. The Middle Way is not the 'middle' or 'average' of ice and water, but the true form of each, H2O, and maintained that the state of nirvana was also like this, a state where the true form of all dualities is revealed as equivalent. stated that this would achieve nothing since the whole point of meditation was to rid one's mind of all divergent thoughts, which was the cause of karmic rebirths and its concomitant suffering, by focusing the mind deeply on only one gong'an until it destroyed all other thoughts. By studying gong'ans like a curriculum, one was only exercising the mind even more, which was diametrically opposed to the original goal of extingishing the mind. Thus, this gradual style of meditation was not only similar to Jinul's gradual cultivation, it was a complete waste of time to the practitioner in that Zen became nothing more than an exercise in sophistry, with higher positions being given to those who could solve more riddles. Gong'ans can never be solved with such rational, or even intuitive methods, and only the final, perfect enlightenment could give the solution to the gong'an, and simultaneously all gong'ans. Therefore, Seongcheol repeatedly made clear that the study of many gong'ans was antithetical to true meditation. He stated that attaining perfect enlightenment was equal to becoming a Buddha, and this was also equal to definitively solving the gong'an, remarking that this was not his unique teaching, but that of numerous masters including Huineng, , all the way down to current masters. Being able to solve multiple gong'ans was pure delusion believed by many practitioners, and Seongcheol devoted much of his teachings to elucidating this point.
Seongcheol played a key role in revitalizing Korean Buddhism which had been in deep disarray from the . He was one of the leaders in the reformation, bringing back celibacy, strict practice, monasticism, and mendicancy back to Korean Buddhism. Later in his life, with his growing recognition, he helped to rectify Buddhism's discredited reputation amongst the general public, from a group of nominal monks who would get married, own businesses, and frequently collude with the Japanese occupiers, to that of serious practitioners, who never got married, and owned no possessions. Seongcheol also contributed significantly to bringing back Huineng's 'sudden enlightenment, sudden cultivation,' and clarified the notions of gong'an practice, meditation, monasticism, and enlightenment. More than a decade after his death, his books are still widely read and respected, and pilgrimages to Haeinsa are a mainstay for Buddhists.