From LTI Korea website:
The world of Ahn Sang-Hak’s poetry is built on the philosophy of non-doing naturalism.
According to this idea, since nature exists, it clearly has substance; however, since its nature is not to stay fixed, but rather to change in every moment, it only appears in variations of itself.
In the same way, all beings appear, change, and disappear, doing so through the operation of the harmony and antagonism between yin and yang.
The book is available from LTI Korea, Kyobo, and elsewhere in Korea, but otherwise hard to obtain outside of Korea.