经曰。心者。生之本。神之变也。肾者。主蛰封藏之本。精之处也。夫神精之用。为人身之大主。精以养神。神藏
于精。而以气行乎其间。惟其有以居之。有以藏之。而人道以立。此心肾所以为人之大主也。阴阳离合论曰。圣人南面
而立。前曰广明。后曰太冲。广明者。心也。居心必于开广之地。清明之座。所以建极也。前之者。神君坐照向明接物
也。然其用为火。火之体亢而不下。若以昭明为事。而无真精真气以养之济之。则必有自焚之患。此太冲之由。未有不
能不为之后焉者也。太冲者、生气之所由来。起升之而不息者也。太冲之地。即为少阴。少阴肾之宅也。肾为先天之根。
藏精之腑。天根之处。乃生气之原。其精内蕴。则其气上腾。故圣人首揭之。以此为养心存神之物。而特云后者。唯此
可奉于前也。然则以精养神。真道自主于肾。而凡储精之处。以为养神者。抑又无所不备。不特太冲之下。脏为精海以
汇之。而又于六阳华盖之上。以太冲之精。结为泥丸髓海。而为玄珠以覆之。又于任处地道之道。复有关元黄庭。孕结
金水之气以蕴之。此正所谓君火之下。阴精承之者也。顾人之心为神之主。前后上下。既能积精以养神。而归于太冲所
起之肾矣。又谓肾为蛰藏之本。惟甚吝啬。此何以言之。盖人之阴精。藏气于肾。而其精泉难充。最后成女子必二七。
男子必二八。而后天癸至。天癸者。非精非血。天乙之真气也。故其至也必久。养之而精血充。充则男子始泻。女子始
月。至其盈数。女子不过七七。男子不过八八。故精难成而易亏。此肾所为蛰藏之官而吝啬也。若使肾家无主。不蛰不
藏。命门水火两亡。则精衰而神耗。精已而神去矣。不特此也。肾之所主。受五脏六腑之精而藏之。必五脏盛乃能泻。
是肾主人身一盘五行之全局。而合之以为精者也。故五脏若有一衰。则肾精即已不茂。盖肾精所以养神而藏气。实以化
精。故曰精食气。气归精也。
《内经》说：心，是生命的根本，也是神志变化所在。肾，主蛰伏封藏，是精气的汇聚之处。神与精的作用，是人体生命活动的主要主宰。精用来滋养神，神潜藏于精中，并通过气在二者之间运行。正因为有地方让神安居，有地方让精封藏，人道才能确立。这就是心肾之所以成为人体主要主宰的原因。
《阴阳离合论》说：圣人面向南方站立，前方称为“广明”，后方称为“太冲”。所谓“广明”，指的是心。心必须居于开阔明亮之地、清明尊贵之位，以此建立至高无上的准则。所谓“前之者”，是指神君端坐照耀，面向光明以接触万物。然而心的功能属火，火的性质是炎上而不下降。如果只追求光明昭著，而没有真精和真气来滋养、济助它，就必然会有自焚的祸患。这就是为什么“太冲”（后方）不能不随之存在的原因。“太冲”，是生气产生的源头，不断升起而不停息的地方。“太冲”之地，就是少阴经，也就是肾的居所。肾是先天的根基，是贮藏精气的脏腑，是天根所在，也是生气的原动力。肾中精气内蕴，则肾气向上腾升。所以圣人首先提出这一点，将其作为养心存神的依据，特别强调后方（肾），因为只有后方的肾精可以奉养前方的心神。
既然用精来养神，那么真道的自主权在于肾，而凡是储存精气的地方，用来养神的，无不具备这种功能。不仅是在太冲之下，脏腑汇聚如精海一样储藏精气；而且在六阳华盖（肺）之上，以太冲的精气凝结为泥丸髓海，形成玄珠来覆盖保护它。又在任脉所行的地道之中，有关元、黄庭等穴位，孕育凝结金水之气以蕴藏精气。这正是所谓“君火之下，阴精承之”的道理。
看人的心是神的主宰，前后上下都能积聚精气以养神，最终归结于由太冲所起的肾脏。但又说肾是蛰伏封藏的根本，非常吝啬，这是什么意思呢？原来人的阴精，将气藏于肾中，但精泉难以充盈。女子要到十四岁，男子要到十六岁，后天癸水才至。天癸，不是精也不是血，而是天乙的真气。所以它的到来需要很长时间。经过调养使精血充盛，充盛后男子才开始泄精，女子才开始行经。到了盈亏的极限，女子不超过四十九岁，男子不超过六十四岁。所以精气难成而易亏，这就是肾被称为蛰藏之官且显得吝啬的原因。如果肾中没有主宰，不蛰伏不封藏，导致命门的水火两亡，就会精气衰败而神志耗散，精竭则神去。
不仅如此，肾所主管的，是接受五脏六腑的精气并加以贮藏。必须是五脏精气旺盛，肾才能排泄（施泻）精气。因此，肾掌管着人身五行全局的一盘棋，并将它们合而为一形成精气。所以，五脏中若有一个衰弱，肾精就会不再茂盛。因为肾精用来养神和藏气，实际上是为了化生精气，所以说“精食气，气归精”。
The *Classic* states: The Heart is the root of life and the residence of spiritual transformation. The Kidney governs hibernation and storage, serving as the repository of essence (Jing). The functions of spirit (Shen) and essence are the primary masters of the human body. Essence nourishes spirit; spirit resides within essence, moving between them through Qi. Because there is a place for spirit to dwell and a place for essence to be stored, the way of humanity is established. This is why the Heart and Kidney are considered the primary masters of the human body.
The *Treatise on Yin-Yang Separation and Combination* states: When a sage stands facing south, the front is called "Guangming" (Broad Brightness), and the back is called "Taichong" (Great Surge). "Guangming" refers to the Heart. The Heart must reside in an open, bright place, in a seat of clarity and nobility, thereby establishing the supreme standard. The "front" refers to the Spirit Lord sitting in illumination, facing the light to interact with things. However, its function belongs to Fire. The nature of Fire is to flare upward and not descend. If one only seeks brightness and illumination without true essence and Qi to nourish and assist it, there will inevitably be the danger of self-incineration. This is why "Taichong" cannot fail to exist behind it. "Taichong" is the source from which vital energy arises, rising continuously without cessation. The land of Taichong is Shaoyin (Lesser Yin), which is the dwelling of the Kidney. The Kidney is the root of pre-heaven existence, the zang organ that stores essence, the place of the heavenly root, and the origin of vital energy. When essence is contained internally, Qi ascends. Therefore, the Sage first highlights this point, using it as the basis for nourishing the Heart and preserving the Spirit. It specifically emphasizes the rear (Kidney) because only the essence of the rear can serve to nourish the spirit of the front.
Thus, since essence nourishes spirit, the autonomy of the true Dao lies with the Kidney. Any place that stores essence to nourish spirit possesses this capability fully. Not only does the area below Taichong, where the zang organs converge like a sea of essence, store it; but also above the "Six Yang Canopy" (Lungs), the essence of Taichong condenses into the "Niwan Marrow Sea," forming a mysterious pearl to cover and protect it. Furthermore, along the path of Renmai (Conception Vessel), there are Guanyuan and Huangting acupoints, which nurture and condense Metal-Water Qi to store it. This is precisely what is meant by "Below the Ministerial Fire, Yin Essence supports it."
Consider that the Heart is the master of Spirit. Whether front, back, above, or below, if one accumulates essence to nourish spirit, it ultimately returns to the Kidney arising from Taichong. Yet, it is said that the Kidney is the root of hibernation and storage, being extremely "stingy." Why is this? Human yin essence stores Qi in the Kidney, but the spring of essence is difficult to fill. For women, Tian Gui (Heavenly Water/Menstruation) arrives only after age fourteen; for men, only after age sixteen. Tian Gui is neither essence nor blood, but the true Qi of Heavenly Yi. Therefore, its arrival requires a long period of cultivation. Once nourished so that essence and blood become abundant, men begin to ejaculate, and women begin menstruation. Regarding their peak and decline, women do not exceed age forty-nine, and men do not exceed age sixty-four. Thus, essence is difficult to form but easy to lose. This is why the Kidney is called the official of hibernation and storage and appears stingy. If the Kidney lacks a master, failing to hibernate and store, leading to the loss of both Water and Fire in the Mingmen (Gate of Life), then essence will decline and spirit will dissipate. When essence is exhausted, spirit departs.
Moreover, what the Kidney governs is receiving and storing the essence of all five zang and six fu organs. Only when the five zang organs are prosperous can the Kidney excrete (discharge) essence. Thus, the Kidney manages the entire game of the Five Elements in the human body, combining them to form essence. Therefore, if any one of the five zang organs declines, the Kidney's essence will no longer be lush. Since Kidney essence nourishes spirit and stores Qi, it essentially transforms into essence. Hence, it is said: "Essence feeds on Qi, and Qi returns to essence."