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The human body is a microcosm. The Qi of heaven and earth does not exceed Yin and Yang. When Yin and Yang are harmonious, then the universe attains clarity and tranquility, abysses and mountains stand firm, and even grasses, trees, birds, and beasts thrive. As stated in the *Yijing* (Book of Changes): "Mountain and marsh communicate with each other; water and fire do not repel each other." This is what is meant by the harmony of Yin and Yang. Therefore, the *Yijing* corresponds to heaven and earth, and thus can encompass the Dao of heaven and earth. In the past, I also held that medicine corresponds to the *Yijing*, and thus can illuminate the origin of opening and closing transformations. The human body possesses five Zang organs, six Fu organs, four limbs, and hundred bones. Without Qi, there is no generation; without Blood, there is no circulation. Qi and Blood belong to the category of Yin and Yang. Medicine seeks Yang within Yin and Yin within Yang, cycling endlessly, turning reversal into compliance, reduction into growth, deficiency into fullness, distinguishing between congenital and acquired origins, examining suitability for dryness and dampness, and observing the application of rigidity and flexibility. Through the mutual assistance of these two Qi, interior and exterior, excess and deficiency are all clearly understood within. Thus, referencing ancient methods can treat contemporary diseases. As it is said, divine illumination depends on the individual. One who is proficient in the *Yijing* is invariably proficient in medicine.

When Ying (Nutritive) and Wei (Defensive) Qi are regulated, meridians and collaterals become smooth; when Yin and Yang are disordered, diseases arise. Xuanyuan (Yellow Emperor) and Qibo possess the miraculous power to restore creation. The *Lingshu* (Spiritual Pivot) and *Suwen* (Basic Questions) are like the sun and moon traversing the sky, or rivers and seas flowing across the earth. Later generations, though exhausting themselves to probe the profound and subtle, still fear their understanding is unclear, leading to improper application of techniques. Only masters such as Zhang Zhongjing, Xue Lizhai, Zhu Danxi, and Li Donglan, who were lucid, enlightened, and spiritually attuned, could penetrate its mysteries. They all produced writings that serve as guides for physicians, gaining fame after Bian Que and Chunyu Yi. Works such as *Yizong Jinjian* (Golden Mirror of the Medical Tradition), *Yilin Cuyao* (Essentials from the Forest of Medicine), *Yitong Zhengmai* (Orthodox Pulse of Medical Orthodoxy), *Bacui Fang* (Extracts from the Pinnacle), and *Baodian* (Precious Mirror) are sufficient to supplement the *Neijing* (Inner Canon), just as the Hundred Schools of Thought cannot be discarded outside the Six Classics. However, these texts are vast and overwhelming; if studied in childhood, one may reach old age without grasping their source. If one could extract the essence, without bias or omission, brilliant as the Milky Way and bright as the stars, enabling readers to cleanse the five Zang organs through reading, refine Jing (Essence) and transform the form, and establish a clear principle, this would indeed be penetrating the mystery of simplicity in the *Yijing* and possessing the merit of assisting in creation.

Mr. Zhang Huiqing of my county, named Jiebin, styled Tongyizi, read widely without exception. In his youth, he enjoyed discussing military strategy and swordsmanship, desiring to contribute to the world. Divining with the *Yijing*, he obtained the hexagram Dun (Retreat) of Heaven over Mountain, and thus resolved to live in seclusion in rocky caves, withdrawing from the world into the gourd (a metaphor for hermitage). He mastered the Dao of Xuanyuan and Qibo. In critical moments of life and death and difficult cases, he examined respiration at the finest degree and distinguished floating and sinking pulses with acute sensitivity. He analyzed the source and flow of Jun (Sovereign), Chen (Deputy), Zuo (Assistant), and Shi (Envoy) herb roles, and thoroughly explored the mysteries of Wang (Observation), Wen (Inquiry), Qie (Palpation), and Wen (Listening/Olfaction). Compiling these into the *Jingyue Quanshu* (Complete Works of Jingyue), organized into Eight Arrays and Nine Palaces, with categories preceding and formulas following, he discarded dross of stale language and elucidated the thoughts of former sages. He referenced conforming theories, dissected doubtful ones, and supplemented brief ones. It is truly a ferry for crossing the world and an elixir formula for preserving health.

This book has been widely praised throughout the land for a long time. I felt regretful for not having seen it until, coincidentally, Lin Ruhui’s nephew brought it to Guangdong, as if obtaining a precious arch-shaped jade disc. I then said to my sons: The benevolence of this great work in aiding the world is no inferior to that of a good minister. How could it be kept private by one person or family? I have therefore commissioned its printing to make it public to the world, hoping not to obscure the author's painstaking efforts, but rather to emulate the transmission of secret prescriptions by Changsang Jun.

Preface by Lu Chao of Kuaiji