The direct seeing of one’s own nature is enlightenment. That is, when all around, inside and out, is bright, and our original mind is clearly illuminated, that direct seeing of that nature, is gyeonseong (seeing the nature). Seeing the nature is enlightenment.
In Patriarchal Seon, that enlightened person is called a mindless person of the Way (musim doin). Gyeonseong (seeing the nature) is the enlightenment to no mind (musim), and that no-mind achieves the content of seeing the nature. Seon Master Huangbo in his Chuanxin fayao (Esssential Dharma of Transmission of the Mind) said the following about the mind of the mindless person of the Way:
There are no minds at all in no-mind. Being a constitution of thusness, internally it is like a tree or a stone, it has no movement; externally it is like open space, there are no borders to block or catch it. Here there is not even the characteristic of a fixed space-time, nothing to be gained or lost.
Huangbo compared the state of no-mind of the mind of a person who had seen the nature to space. The characteristic of space is the mind of that enlightened person. Space has no increase or decrease, no coming or going, no birth or extinction. It, as mind, is inconceivably boundless and apart from all value judgments.
Similarly, our self-nature also is originally pristine, vacant and empty, and the myriad dharmas are held within it. Inside the mind of sentient beings and the mind of the Buddha there is provided the wisdom of prajñā, which illuminates everything everywhere. Although it is such a light of wisdom, the mind of sentient beings is hidden by the clouds of frustration and is attached to the realms that appear as reality. This is delusion. We are hidden by this delusion and cannot see directly the pristine self-nature.
If we see the nature and become enlightened, what will become of us? In the Platform Sutra of the Sixth Patriarch it says that if we see the nature we will live a life through no-thought. No-thought is not an i-nyeom (apart from thought) that is no thinking at all. No-thought is while one is thinking one is not caught up in thought.
A person of the Way who sees the nature in this way, even though he thinks, sees the nature because he lives through no-thought that is not entangled in that thought, and can only be different to lives that cannot (see the nature). Sentient beings who cannot see the nature are trapped in thought and objects, and although they lead a life restrained by being attached to them, the person of the Way who sees the nature lives a life of genuine freedom without any obstacles.
An enlightened person is one who is free and autonomous anywhere and at anytime. Although they live a life all day long in which there is an image of the self that discriminates I and you, they were not caught up in that fact. An enlightened person is not a person who has the power to willfully change external conditions or the surrounding environment, or use miraculous powers or the most fantastic force of the Way. They also, like ordinary people, eat, sleep and act. However, because there is a difference in appreciation before seeing the nature and after seeing it, their life must be different from that of ordinary people. This is because the eye that looks at life and the world has changed.