越人谓左为肾，右为命门，非也。命门即在两肾各一寸五分之间，当一身之中，《易》所谓一阳
陷于二阴之中，《内经》曰七节之旁，中有小心是也。名曰命门，是为真主乃一身之太极，无形可
见，两肾之中是其安宅。
三焦是其臣使之官，禀命而行，周流于五脏六腑之间而不息，名曰相火。相火代天行化。此先天
无形之火，与后天有形之火不同，出之右旁小窍者也。
其左旁亦有小窍，乃真阴真水气也，亦无形，上行夹脊，至脑中为髓海。泌其津液，注之于脉，
以荣四末。内注五脏六腑，以应刻数。常随相火而潜行于周身，与后天有形之水不同。
但命门无形之火，在两肾有形之中，为黄庭，故曰五脏之真，惟肾为根。可见命门为十二经之主。
肾无此则无以作强，而技巧不出矣；膀胱无此则三焦之气不化，而水道不行矣；脾胃无此则不能蒸腐水谷
，而五味不出矣；肝胆无此则将军无决断，
而谋虑不出矣；大小肠无此则变化不行，而二便闭矣；心无此则神明昏而万事不能应矣，正所谓主不明则
十二官危也。譬之元宵之灯，鳌山走马，拜舞飞走者，无一不具，中间惟是一火耳。火旺则动速，火微则
动缓，火熄则寂然不动。而拜舞飞走者，躯壳未尝不存也，故曰此身非汝有，是天地之委形也。
夫水为立命之门，乃人身之至宝，何世之养身不知节欲，保真水以全火，而日夜戕贼。此火既病矣，
治病者不知温养
此火，而日用寒凉以直灭此火，焉望其有生气耶？
余今直指其归元之路。夫命门真主之火，乃水中之火，相根据而永不相离者也。火之有余，缘真水之
不足也，毫不敢去火，只补水以配火，壮水之主，以制阳光；火之不足，因见水之有余也，亦不必泻水，
就于水中补火，益火之原，以消阴翳。所谓原与主者，皆属先天无形之妙，非曰心为火而其原在肝，肾为
水而其原属肺之谓也。
若夫风寒暑湿燥火六者之入于人身，此客气也，非主气也。主气固，客气不能入。医家徒知客者除之
，慢不加意于主气。纵有言固主气者，专以脾胃为一身之主，焉知坤土是离火所生，而艮土又属坎水所生耶？
故此一水一火，俱属无形之气，相火禀命于命门，真水又随相火，自寅至申，行阳二十五度，自酉至丑，
行阴二十五度，周流于脏腑之间，滞则病，息则死矣。故曰∶先天惟此一火克全。此火而归之矣。
扁鹊（越人）认为左边是肾，右边是命门，这种说法是不对的。命门位于两肾之间各一寸五分的地方，正对人体的中心，正如《易经》所说的“一阳陷于二阴之中”，《黄帝内经》所说的“第七节旁边，中间有小心”指的就是这个部位。命名为命门，它是真正的君主，是一身的太极，没有具体的形象可见，两肾之中就是它的居所。
三焦是执行命令的臣使之官，秉承命门的指令而行事，在五脏六腑之间循环流动而不停止，称为相火。相火代天施行生化功能。这是先天的无形之火，与后天的有形之火不同，是从右侧旁的小窍发出的。
左侧旁也有一个小窍，那是真阴真水之气，也是无形的，向上沿着脊柱两侧运行，到达脑部成为髓海。它分泌津液，注入脉中，以滋养四肢末端。向内灌注到五脏六腑，以对应时间的刻度。它常常随着相火在周身潜行，与后天的有形之水不同。
然而命门无形的火，存在于两肾有形的组织之中，被称为黄庭，所以说五脏的真气，唯独以肾为根本。由此可见命门是十二经脉的主宰。肾如果没有这火就无法发挥作强之功，技巧也就无法产生；膀胱如果没有这火，三焦的气化功能就会失常，水道也就不能通行；脾胃如果没有这火，就不能蒸腾腐熟水谷，五味也就无法化生；肝胆如果没有这火，将军（肝）就缺乏决断力，谋虑也就无法产生；大小肠如果没有这火，变化传导功能就不能进行，二便就会闭塞；心如果没有这火，神明就会昏昧，万事都不能应对了，这正是所谓“主不明则十二官危”。这就好比元宵节的灯彩，鳌山走马灯上各种拜舞飞走的形象无一不备，中间仅仅是一团火罢了。火旺则转动迅速，火微则转动缓慢，火熄灭则静止不动。而那些拜舞飞走的形象，躯壳并未消失，所以说这身体不属于你，而是天地寄托的形体。
水作为立命的门户，是人身的至宝，为什么世上养生的人不知道节制欲望，保全真水以护持真火，反而日夜伤害自己？这火一旦生病，治病的人不知道温养这火，反而日常使用寒凉药物直接扑灭这火，哪里能期望它有生机呢？
我现在直接指出回归本源的道路。命门真主的火，是水中之火，与水相互依存而永远不分离。火的有余，是因为真水的不足，所以不敢去火，只补水以配合火，即“壮水之主，以制阳光”；火的不足，是因为看到水的有余，也不必泻水，就在补水中补火，即“益火之原，以消阴翳”。所谓原和主，都属于先天无形的奥妙，不是说心为火而其原在肝，肾为水而其原属肺的意思。
至于风、寒、暑、湿、燥、火这六种邪气侵入人体，这是客气，不是主气。主气坚固，客气就不能侵入。医生只知道去除客邪，却慢慢忽视了对主气的养护。即使有人提到要固护主气，也专门以脾胃为一身的主宰，哪里知道坤土（脾）是由离火（心）所生，而艮土（胃/大肠等）又属于坎水（肾）所生呢？
所以这一水一火，都属于无形之气，相火禀受命门的指令，真水又跟随相火，从寅时到申时，行于阳分二十五度，从酉时到丑时，行于阴分二十五度，周流于脏腑之间，停滞就会生病，停止就会死亡。所以说：先天只有这一把火能够成全一切。这把火归于命门了。
Yuèrén (Bian Que) stated that the left is the Kidney and the right is the Mingmen (Gate of Life), which is incorrect. The Mingmen is located between the two Kidneys, one cun and five fen from each, corresponding to the center of the body. This aligns with the *I Ching*’s description of "one Yang trapped within two Yins," and the *Neijing*’s statement: "Beside the seventh vertebra, there is a small heart." It is named Mingmen, serving as the true Sovereign, the Taiji of the entire body. It has no visible form; its dwelling place is within the two Kidneys.
The Sanjiao (Triple Burner) acts as the ministerial envoy, executing orders and circulating ceaselessly among the Zang and Fu organs, known as Xianghuo (Ministerial Fire). Xianghuo performs transformations on behalf of Heaven. This is the pre-natal invisible fire, distinct from post-natal tangible fire, emerging from a small aperture on the right side.
On the left side, there is also a small aperture, through which Zhenyin Zhen Shui (True Yin and True Water) Qi ascends along the spine to the brain, becoming the Sea of Marrow. It secretes fluids, injects them into the vessels, and nourishes the four extremities. Internally, it irrigates the Zang and Fu organs, responding to temporal cycles. It typically follows Xianghuo in covert circulation throughout the body, differing from post-natal tangible water.
However, the invisible fire of the Mingmen resides within the tangible tissues of the two Kidneys, referred to as Huangting (Yellow Court). Thus, it is said that the true essence of the five Zang organs finds its root in the Kidney. Consequently, the Mingmen is the master of the twelve meridians. Without this fire, the Kidney cannot perform its function of strength and skill; without it, the Bladder lacks the Qi transformation of the Sanjiao, causing the water passages to stagnate; without it, the Spleen and Stomach cannot steam and rot food and drink, failing to produce the five flavors; without it, the Liver (General) loses decisiveness and planning; without it, the Large and Small Intestines lose their transformative functions, leading to constipation or incontinence; without it, the Heart’s Shen (Spirit) becomes dim, unable to respond to affairs. This is precisely what is meant by "if the Sovereign is unclear, the twelve officials are in danger." Consider the lanterns during the Lantern Festival or the walking horse lanterns: all figures are present, but at the center is merely fire. When the fire is strong, movement is fast; when weak, slow; when extinguished, stillness prevails. Yet the bodies of the figures remain intact. Thus, it is said: "This body does not belong to you; it is a form entrusted by Heaven and Earth."
Water serves as the gate of establishing life, the supreme treasure of the human body. Why do people today, seeking health, fail to restrain desires and preserve True Water to safeguard True Fire, instead harming themselves day and night? Once this fire is diseased, physicians often neglect to warm and nourish it, instead using cold and cooling herbs daily to extinguish it directly. How can one expect vitality under such conditions?
I now point directly to the path of returning to the source. The fire of the Mingmen’s true Sovereign is fire within water, inseparable from water. Excess fire stems from a deficiency of True Water; thus, one dare not eliminate fire but should tonify water to harmonize with fire—"Strengthen the master of water to control excessive yang." Deficiency of fire appears as excess water; thus, one need not drain water but should tonify fire within the context of water—"Benefit the origin of fire to dissipate yin shadows." The terms "origin" and "master" refer to the profound mysteries of pre-natal invisible qi, not implying that the Heart is fire with its origin in the Liver, or that the Kidney is water with its origin in the Lung.
Regarding the six external pathogens—Wind, Cold, Summerheat, Dampness, Dryness, and Fire—they are guest qi, not host qi. If host qi is solid, guest qi cannot enter. Physicians only know how to expel guests but neglect to strengthen host qi. Even those who advocate strengthening host qi focus solely on the Spleen and Stomach as the center of the body, failing to realize that Kun Earth (Spleen) is generated by Li Fire (Heart), and Gen Earth (Stomach/Large Intestine) is generated by Kan Water (Kidney).
Therefore, this water and fire both belong to invisible qi. Xianghuo receives orders from the Mingmen, and True Water follows Xianghuo. From Yin hour to Shen hour, it circulates twenty-five degrees in the Yang aspect; from You hour to Chou hour, it circulates twenty-five degrees in the Yin aspect, flowing continuously among the Zang and Fu organs. Stagnation leads to disease; cessation leads to death. Hence it is said: "In the pre-natal stage, only this single fire can complete everything." This fire returns to the Mingmen.