Both small water wheel and big water wheel are the creation and presentation when the small universe of the human body begins to communicate with the big universe. The great internal alchemist Zhang San Feng likened people’s physical body to a tree that has no root and things may go worse than that: the human body even do not have the qualification in comparison with the weed who often die away year on year but keep their roots deep in earth when the winter days come. It begin to flourish again when Spring unveils her charm again. In such respect, how human body can compete? In this respective, we can understand how shortly the people’s life span is. The following passage from Chuang Tzu can vividly describe the people’s whole like time:
"Man's life between heaven and earth is like the passing of a white colt glimpsed through a crack in the wall‑whoosh!‑-and in an instant coming to an end. Overflowing, starting forth, there is nothing that does not come out; gliding away, slipping into silence, there is nothing that does not go back in. By a transformation they live, and by another transformation they die. Living things grieve over it, mankind sheds tears for it.
Therefore, the people should learn to imitate the living style from the weed? If so, how, you may ask? Learn how to return to the very root for keeping the life force which is at the very base level.
Therefore, there comes the popular saying: going along the life course to become a human being whereas going against the life currents to accomplish the immortality. We well understand that corporeal immortality is impossible because the physical body only serves as a temporary carrier or nest like the butterfly that is metamorphosesed from chrysalis who, accordingly, is developed from a larva.
Water can demonstrate itself in a wealth of presentation forms (waves, ice, currents, drops, rain, due) but the essential of it remains the same --- water. All myriads of things are but the mythical transformations from the very common one and there is no any exception. Yet, still people do not acknowledge it and refuse to accept such fact. Some people with belief of philosophy of materialism hold that only materialism bear something meaningful. Here we borrow some words from Chuang Tzu to help such people understand more:
"Well indeed" answered Lien Shu, "We cannot expect a blind man to appreciate beautiful designs, nor do we expect a deaf man to enjoy the music from bells and drum. Not only are there the physical blindness and deafness, there also exist the intellectual blindness and deafness!
How to go against the life currents to accomplish the immortality, you may ask? Learn the example the weed makes. Then Lao Tzu (Tao Teh Ching) offered his idea for the returning process in chapter 16:
To quiet down the heart to stay at a constant stillness,
To settle down the heart to remain in an infinite emptiness,
All the myriad things are involved in constant motion, but I just gaze into emptiness to unintentionally wait for the coming of the Mysterious Pass.
Yes, though all things flourish with myriad variations, each one will eventually return to the very root of birth and death.
To return to the root needs constant stillness.
Only by staying in a constant stillness can pre-heaven nature be recovered.
To fully recover pre-heaven nature is called Chang.
To know Chang is called “enlightenment.”
To not know Chang and to act blindly will result in disaster.
Only knowing “Chang” one can tolerate all,
Only tolerating all one can be impartial.
By being impartial one can be all accommodating,
By being all accommodating, one can equal Heaven,
By equaling Heaven, one can accomplish Tao, which lasts without death.
Only by accomplishing Tao can one be rid of death and birth,
lasting eternally without any danger.
Such chapter offers an outline as to the process regarding to return to the very root of both birth and death which is termed as Mysterious Pass. Once you follow the sequence to get close the the Mysterious Pass the division between the artificial and the natural get blurred and die out. So, it is complete chaotic state (people may think you are sleeping but it is not). Therefore, by approaching to the Mysterious Pass and dwelling in it (you do not know how) you are in the process of adhering to the very root. Please read the following chapter 25 from Tao Teh Ching for more reference:
There was something naturally formed as infinite achromatic chaos, long before Heaven and Earth.
Boundlessly still and desolately comprehensive, it remains unchanged and independent ever since, functioning in all in a thoroughly-going way without any lapse.
One can regard it as the mother of everything.
I do not know its name,
In a farfetched way I name it as Tao,
In a farfetched way I term it as Greatness.
Terming it as Greatness, because it transcends all,
Terming it transcending all, because it exhausts infinitude,
Terming it exhausting infinitude, because it is contained in all.
Therefore Tao is great,
Heaven is great,
Earth is great,
Sage is great,
There are altogether four greatness in the nameless realm,
The Sage is one of them.
Man follows the way of Earth,
Earth follows the way of Heaven,
Heaven follows the way of Tao,
Tao is characteristic of the great Natural Way.
Therefore, by following the example of Earth people become firm, quiet and gradually get detached from the accustomed attachment to the cognizing objects. By following the example of Heaven the weight of physical body becomes to lose its weight little by little --- spacious and empty. Heaven and Earth give arise to myriads of things in its style and it is a very spontaneous process---it is Tao. Only via the detachment the independence can gained little by little. Just such the initial process has to get small water wheel and large water wheel involved.
The small water wheel (Du channel along the back and Ren channel in front combine to form a circle) comes into being because Qi begins to circulate. Large water wheel is a big circle reaching as far as to the acupoint of YongQuan (the center points of two feet), which mostly is the circulation of Shen. In fact, to communicate with the outside universe both small water wheel and large water wheel play an critical role. People should understand the small universe of human body is a decayed system and do not have the qualification to sit side by side with outside universe. So, in I-Ching theory there came the theory of Pre-heaven trigrams and Post-heaven trigrams which are used to demonstrate the difference between the two system. First is to open the decayed system, then invite the pre-heaven elements (Qi and Shen) to gradually transform the post-heaven system. In taoism theory there exists the popular saying of ‘two layers of Heaven and Earth and four kinds of Yin and Yang’ which demonstrate such communication procedure.
Now let go further to the details of small water wheel. There are much metaphor used to illustrate the procedure of small water wheel (you can find lots in the book “Understanding the Reality”). To tell the truth, they cannot go beyond the scope of transforming the Post-heaven trigrams back to Pre-heaven trigrams and mostly the maneuvering of four emblematic symbols. Therefore, things begin to be be made more and more secretive and mythical by some scholars in this regard and some terminology as lead, mercury, virgin body, middle-woman, moon rabbit, gold father, wood mother, etc start to confuse people’s mind continuously from the very ancient time to nowadays. I think, in the future it will persist to try people’s mind and test their wisdom.
Yes, the description is correct in theory. But the point is in Pre-heaven state there is no any mind or idea to manipulate (do you think the Heaven and Earth have mind to do something) anything yet everything seems to be well done. In Post-heaven state all people want to accomplish something with their wisdom yet nothing is perfectly done. During the reversing process the manipulation should go as before, you may ask? To get a correct answer to this question to have to understand what is Wu earth and what is Ji earth (the true intention and the dissipated intention). It is s long talk and here I have to cut it short. To successfully reverse to the Pre-heaven state the people have to let the very natural to preside over the artificial (we cannot kill our mind or destroy it completely). So, under such principle you can well understand the goings are that initiated by the very natural rather than the artificial and the artificial really has no any qualification to finish this job. Here people can understand how is YouWei --- doing something with intention and WuWei--- action without action" or "effortless doing.” So, you can get the answer as to how to proceed correctly with your practice. But, really there is no any role involved with the artificial? It would be completely wrong if you really think so.
Yes, we have to confess some Kungfu practitioners want to accomplish some special power by deploying the Qi in a special way. This is another arts and it differs very much from what I am talking about. So, please do not add such argument to refute.