Below is one zen koan by one enlightened master.
Before I practise Zen, I saw mountains as mountains, and waters as waters.
When I arrived at a more intimate knowledge, I came to the point where I saw that mountains are not mountains, and waters are not waters.
But now that I have got its very substance I am at rest. For it's just that I see mountains once again as mountains, and waters once again as waters.
My answer :-
1. I saw mountains as mountains, and waters as waters.
This statement #1 is referring to what normal people (unenlightened) is seeing when they are looking at FORMS. FORMS are objects that have appearance, like mountain, trees, birds, cloud, cars, rivers, buidlings, etc... Human in samsara has attachment to forms, thus they see FORM as FORM, mountain as mountain, water as water.
2. When I arrived at a more intimate knowledge, I came to the point where I saw that mountains are not mountains, and waters are not waters.
Statement #2 is when someone has understood the true nature of all phenomena and dharma as "emptiness", which is the nature of all forms. Example ice. Ice has form or appearance. When it melts into water, water also has form or appearance. But when water evaporates into water vapour, water vapour has no form or appearance (we cannot see water vapour) which is comparable to "emptiness". We all know in science that ice, water or vapour are the same i.e. they are a compound of two hydrogen atoms and one oxygen atom.
In Chemistry, we studied that atoms are still not the smallest particles. When atoms are divided, there are make up of protons, electrons, and neutrons. Scientist have also discovered that neutrons, electrons, and protons are make up of even smallest particles like quarks. Scientists believe that if quarks can be further divided, they might finally reach a stage of "emptiness".
Thus, all forms has a nature of "emptiness". FORMS are manifestations while "emptiness" is their basic nature. In the "HEART SUTRA", it says : "forms is emptiness, emptiness is form; form does not differ from emptiness, emptiness does not differ from form".
The first statement "form is emptiness, emptiness is form" implies that the basic nature of form is emptiness, thus form is emptiness. Based on this statement ALONE, one might mistaken form and emptiness are two different thing. Therefore, the second statement "form does not differ from emptiness, emptiness does not differ from form" implies that form and emptiness are actually ONE (they do not differ from each other, they are the same and ONE); not two different things. Form is a manifestation (ice, water) while emptiness (water vapour or H-2-O) is its nature. I am using vapour to represent "emptiness" for easy understanding by everyone because water vapour is invisible and formless.
In addition, a mountain is seen as mountain from afar, but when one walk up on the mountain, the mountain is just accumulation of sands, stones, rocks, mud, grass, etc... When all these sands, stones, rocks, muds, grass, etc... are removed, there is no such thing as mountain; it is only by name called "mountain". Thus, the FORM of a mountain is "emptiness". (Pls note that emptiness does not mean nothingness or annihilation)
Thus, with true understanding of form and emptiness, one sees mountains as not mountains, waters as not waters.
This is a stage where one has no attachment to form.
3. But now that I have got its very substance I am at rest. For it's just that I see mountains once again as mountains, and waters once again as waters.
This last statement is when one has realised, enlightened or awakened to one's self nature. Some school called it Buddha nature, others called it, True Mind / Pure Mind / Bodhi Nature while some called it True Self / Real Self. These are just different names but they all mean the same thing.
One who has not realise his Buddha Nature is like one who is lost in the jungle not knowing where his home is. He is lost in the jungle of illusionary thoughts, fluttering emotions, likes and dislikes, etc...
When one has realised one's Buddha Nature, he is "at rest" like someone who has found and is resting at home. There is no more illusionary thoughts, emotions, greed, etc... He will then discover that all mountains, water, clouds, birds, cars, trees, flowers that he sees are just manifestation of his Buddha Nature. Therefore he will "see mountains as mountains, and waters as waters" again.
One can compare this Buddha Nature to a mirror. If you place a flower in front of mirror, the mirror will manifest the flower exactly as it is. If it is a mountain, the mirror will manifest the mountain.
Everything that we see in this world are just images manifested by our buddha nature, like a huge mirror manifesting all the images of the objects we are seeing. Thus, ALL (the world) is ONE (buddha nature), and ONE is ALL. If you can understand this, you’re ENLIGHTENED.
Not only FORM is emptiness, feeling, thoughts, taste, consciousness are also emptiness. (pls read The Heart Sutra) All these are also manifestations of our buddha nature. For example feelings, when one is happy or joyful, can one show me the thing happiness or joy. Cannot - why? Because their nature are emptiness. They do not have any trace. They are just manifestations. Their arising and ceasing are illusive and emptiness. Do not react to them or get carried away by them. Those that are illusive has arising and ceasing, but the one that is REAL and TRUE has NO arising and NO Ceasing, which is our TRUE MIND. In Vajra Sutra, it states :
"Subhuti, what do you think, is it possible to see the Thus Come One in his physical appearances?" "No World Honored One, it is not possible to see Thus Come One in his physical appearances. Why? Because the physical appearances mentioned by the Thus Come One are not physical appearances." The Buddha said to Subhuti, "All appearances are empty and false. If one sees all appearances as no appearances, then one sees the Thus Come One."
At this stage one has NO attachment to form and emptiness, self-ego (clinging to a self), thoughts and dharma, including the practice of "no attachment". You are what you are because you have realised who you really are. ALL is ONE and ONE is ALL.
In Vajra Sutra, it said :
"If they cling to appearances of dharmas, that would be attachment to a self, others, living beings and a life. Why? If they cling to the appearances of non-dharmas, that would be attachment to a self, others, living beings and a life. Therefore, you should not cling to dharmas; you should not cling to non-dharmas. Because of this principle the Thus Come One always says, 'Bhikshus, you should all know that the Dharma I speak is like a raft. You must let go of dharmas. Even more so let go of non-dharmas.'"
"Subhuti, suppose someone were to fill measureless asamkhyeyas of world systems with the seven precious jewels and give them as an offering. Further, if a good man or good woman who has resolved his mind on Bodhi were to receive, uphold, read or recite and extensively explain for others as little as four lines of verse from this Sutra, the latter person's blessings would surpass those of the former person. "How should this Sutra be explained for others? By not grasping at appearances and being in unmoving thusness. Why? All conditioned dharmas Are like a dream, an illusion, a bubble or a shadow, Like dew or like lightning flash. Contemplate them thus."
At that time the World Honored One spoke a verse saying, One who looks for me in forms, Or seeks me in sounds, practices a deviant path and will never see the Thus Come One.