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Ancient sages said, "If one cannot serve as a virtuous prime minister, one should become a skilled physician." This is indeed because saving the world and benefiting people is the most urgent task. A virtuous prime minister brings peace to the world; a skilled physician benefits people from villages to the entire nation, leaving no one unaided. Although seclusion and public service differ, spreading one's reputation in one's time and achieving immediate results are also matters that gentlemen devote themselves to and dare not neglect. However, those who practice this art must explore its profound mysteries and gain insight into the inner workings of the body; otherwise, how can they lightly attempt treatment? When I was young, I read the *Ling Shu* (Spiritual Pivot, part of the *Huangdi Neijing*), marveled at its metaphors of deep abysses and floating clouds, and immediately felt overwhelmed like someone gazing at the ocean, akin to the confusion of He Bo (River God) when he first encountered the sea!

Mr. Cheng Zhongling, originally named Shanling, possessed high intelligence and extensive scholarship. He devoted himself to civil service examinations and gained renown in local academies. Later, due to poverty and the need to properly support his parents, he turned to studying Qihuang texts (classical Chinese medicine works), pondering them repeatedly. He integrated and mastered the theories of the Four Great Masters: Zhang Yuansu, Liu Wansu, Li Dongyuan, and Zhu Danxi. For every book he read, he made independent judgments, refusing to follow superficial rhetoric to deceive contemporaries. Consequently, when he began practicing, visitors came daily without fail. Year after year, he often hosted patients from distant places for overnight stays. Those who sought his help usually left satisfied. He regretted not having a long tongue to transform into thousands of bodies to meet everyone's needs. Thus, he wrote the book *Yixue Xinwu* (Medical Insights), teaching it to his students. His words were well-founded, and his writing effectively conveyed his ideas, attracting more and more students from all directions. He once told his disciples, "A pot of ice and three hu of fire depend entirely on appropriate usage." However, superior physicians treat disease before it manifests, while average physicians treat it after it has appeared. In ancient times, Yi Huan had three brothers; his two elder brothers treated diseases before they took visible form. Although their fame did not spread among feudal lords, their learning was profound. Chapters such as *Song of Hundred Errors* and *Ginseng Fruit* in the book go beyond mere prescriptions; they aim to prevent disasters before they sprout and ensure livelihoods, which is not empty talk. The money earned daily was mostly used to prepare pastes and powders, available for anyone to take, with frequent efficacy. In remote areas, there were cases where one dose shared by two people yielded results. These pastes remove wind-toxins and various ailments; applied to affected skin, they eliminate symptoms, earning widespread praise. Is this merely false reputation captivating people? Over recent years, funds were distributed immediately, always dedicated to this cause, rivaling figures like Cui Shiming and Li Qingosi. During consultations, regardless of wealth or status, he treated patients meticulously, examining conditions thoroughly and prescribing medications appropriately. His vision flowed everywhere, driven solely by a practical desire to save lives. Many copied and read his medical writings. Fearing limited dissemination, he arranged for printing to share with like-minded individuals. Does this not make him as competent as those who govern and harmonize the state, leaving no regrets? He said, "With the book completed, my burden is somewhat lightened, and I have no further internal worries." I still disagree. Ancient benevolent sages and worthy men dedicated themselves to saving the world, grounding their efforts in reality. The benefits they bring are not empty words; extending from kin to strangers, from near to far, you will see your impact manifest. There is no need to seek elsewhere. As for the profound intent of this book, ashamedly, I am not Bian Que (Yu Ren), unable to fully fathom its depths. I can only observe your intentions and actions from the side and speak plainly, awaiting discerning people of the world to appreciate it together. This is the preface.

Written respectfully by Rao Zhaoxiong, classmate and brother-in-law, at Tianning Zen Monastery, in the early spring of the Renzi year of the Yongzheng era.