Enlightenment means seeing through to your own essential nature and this at the same time means seeing through to the essential nature of the cosmos and of all things. For seeing through to essential nature is the window of enlightenment. One may call essential nature truth if one wants to. In Buddhism from ancient times it has been called suchness or Buddha-nature or one Mind. In Zen it has been called nothingness, the one hand, or one's original face. The designations may be different, but the content is completely the same.
We can say this about Zen: it is a practical method of realizing this buddha-nature.
People today believe they can be enlightened by only studying a few sutras, believe they can be enlightened! How terribly wrong they are!
Without understanding one's mind, memorizing groundless phrases is useless. To seek Buddha, see the self-nature! Self-nature is Buddha!
From Zen's beginning with Bodhidharma we see its core teaching: Enlightenment is available to anyone if only they can experience the intrinsic state of the mind, which is pure and inherently enlightened. This inherently enlightened mind, characterized by total freedom from all discriminating conceptual thought, delusions, and negative emotions, is called Buddha-nature or Buddha-mind.
How wonderful, how surprising! All the beings are already endowed with the wisdom of the Buddha! They have already all Buddha-qualities! How mysterious is it!
Sun and clouds, mind and thoughts
An image often used to describe the ultimate nature of pure mind ("suchness") is the sun, which is always shining. The mind's relative or conventional nature is like clouds, delusion and negativity obscuring the light of the sun.
The sun shines day after day without fail, yet if clouds appear to make the sky overcast, it can't be seen. It still comes up in the east every morning and goes down in the west. The only difference is that you can't see it because it's hidden behind the clouds. The sun is your Buddha-mind, the clouds are your illusions. You are unaware of your Buddha-minds because they're covered by illusions and can't be seen. But you never lose them, not even when you go to sleep
Obey the nature of things
Obey the nature of things (your own nature) and you will walk freely and undisturbed.
Seeing into one's own nature (jian-xing) emerged explicitly as the essence of the Zen teachings and practice. Nevertheless, as we shall see in this course, Zen masters taught different approaches to "seeing" the Buddha-nature immanent in all things.
Why do our minds not dwell in their intrinsically pure state? If our Buddha-mind is intrinsically pure, why do our minds not "see" purely? And what are we to do about the defilements of the mind?
Our body is the Bodhi-tree
And our mind a mirror bright.
Carefully we clean them hour by hour
And let no dust alight.
There is no Bodhi-tree
Nor stand of a mirror bright.
Since all is void
Where can the dust alight?
We shall see that Zen teachers approached this question in many ways. Does one need to actively practice to rid the mirror-like pure mind of impurities, or are the seeming impurities essentially unreal? Must one meditate for a long time to clear one's mind of delusion, or does one simply learn how to dwell in the mind's natural state? Is the dwelling in Buddha-mind a distant goal we can only achieve gradually after a lifetime (and perhaps lifetimes) of practice and study, or is our intrinsic Buddha-mind not something we need to strive to realize but rather immanent? These questions lie at the heart of our stories of Zen.
The Buddha-mind is inherent in people from their parents. Nothing else is inherent. The Buddha-mind inherent from their parents is unborn; it enlightens the mind.