Monk Jinul was a monk who lived under the military regime of the Goryeo Dynasty.
At that time, Goryeo Buddhism flourished as a Buddhism centered on doctrine, so even if one wanted to learn Seon, there were no teachers, so one had no choice but to study on one's own.
Although Guksa was well-versed in Buddhist doctrines to the point of passing the state examination held at the time, he could not stop his search for the origins, so he studied various Zen schools and finally, after reading the Sixth Patriarch's Platform Sutra, his mind became clear.
The monk wanted to share these experiences with his disciples, so he developed the Jeonghye Gyeolsa Movement and wrote this Susimgyeol as a guideline to use as a teaching material for his followers.

This one book clearly explains why we must seek enlightenment, what enlightenment is, and how to practice it afterward.
The Secret of Purifying the Mind, Susimgyeol, is a well-organized text that can be used to purify the mind and achieve the Bodhisattva path with just this one book, and it is also well-known to Buddhist scholars in Western society.
I have no doubt that if you practice according to the teachings of this article, the mind of the Buddha will inevitably be revealed through your body.