东亭先生，是安徽休宁县凤湖人。他一生心地纯正，喜好积累功德、践行善行，丝毫不将功名利禄放在心上。
如今他去世了，竟到了这般地步。家父回答说：“虽然《阴符经》和《道德经》流传于世，但文辞古奥深涩，学习者阅读后往往不能理解；后来炼丹的经书接连出现，内容半隐半露，学习者参悟后也不能透彻明白。这并不是‘道’无法施行，实在是因为‘道’没有被阐明清楚啊。”
先生因此大发慈悲心，撰写了《性命要旨》一书。书成之后，拿给我（柯兆平）看并诵读，书中全是关于先天大道的论述，以及身心性命的学问。自古以来圣贤、仙人、佛陀的心意都是心心相印、口耳相传的秘诀，在这里无一不被彻底阐发出来。这确实是宇宙间的金科玉律，天地之间的宝贵奇文。
诚心诚意追求修真境界的君子，若有缘遇到这本书，就可以登堂入室，遵循书中的方法去实践，层层深入通达，节节都有验证。到那时才会知道先生的道行高深，先生的恩德深厚，而天下后世的学者无不沾受先生的恩泽。
时光绪丁亥年（1887年）初冬月，富川愚侄柯兆平叩首恭敬作跋。
Mr. Dongting was from Fenghu, Xiuning County, Anhui Province. Throughout his life, he maintained a pure heart and was fond of accumulating merit and practicing good deeds, never letting fame, success, or wealth weigh on his mind.
Now that he has passed away, it has come to this. My father replied, "Although the *Yinfu Jing* (Classic of the Hidden Talisman) and the *Daode Jing* (Classic of the Way and Its Virtue) have been handed down through generations, their language is ancient and obscure; students read them but fail to understand. Later, alchemical scriptures emerged one after another, with meanings half-hidden and half-revealed; students pondered them but could not penetrate their essence. This is not because the Dao cannot be practiced, but rather because the Dao has not been made clear."
Therefore, moved by great compassion, Mr. wrote the book *Xingming Yaozhi* (Essential Principles of Nature and Life). Upon its completion, he showed it to me, Zhao Shou, for reading. It is entirely about the Great Dao of the Pre-Heaven state and the study of body, mind, nature, and life. The secrets that sages, immortals, and Buddhas have transmitted heart-to-heart and mouth-to-ear since ancient times are all thoroughly elucidated here. Truly, it is the golden rule of the universe and a precious, extraordinary text within heaven and earth.
Gentlemen who sincerely seek cultivation and truth, if they have the affinity to encounter this book, can enter the inner chambers of learning, follow its methods in practice, penetrate layer by layer, and see verification at every stage. Only then will they realize how profound Mr.'s Dao is and how rich his virtue, and how all scholars of the world and future generations will benefit from his grace.
In the first month of winter in the Dinghai year of the Guangxu era [1887], your humble nephew Ke Zhaoping from Fuchuan bows respectfully to add this postscript.