Zazen just lets people illumine the mind and rest easy in their fundamental endowment. This is called showing the original face and revealing the scenery of the basic ground. Mind and body drop off, detached whether sitting or lying down. Therefore we do not think of good or bad, and can transcend the ordinary and the holy, pass beyond all conception of illusion and enlightenment, leave the bounds of sentient beings and buddhas entirely.
So, putting a stop to all concerns, casting off all attachments, not doing anything at all, the six senses inactive - who is this, whose name has never been known, cannot be considered body, cannot be considered mind? When you try to think of it, thought vanishes; when you try to speak of it, words come to an end. Like an idiot, like an ignoramus, high as a mountain, deep as an ocean, not showing the peak or the invisible depths - shining without thinking, the source is clear in silent explanation.
Occupying sky and earth, one's whole body alone is manifest; a person of immeasurable greatness - like one who has died utterly, whose eyes are not clouded by anything, whose feet are not supported by anything - where is there any dust? What is a barrier? The clear water never had front or back, space will never have inside or out. Crystal clear and naturally radiant before form and void are separated, how can object and knowledge exist?
This has always been with us, but it has never had a name. The third patriarch, a great teacher, temporarily called it mind; the venerable Nagarjuna provisionally called it body - seeing the essence and form of the enlightened, manifesting the bodies of all buddhas, this, symbolized by the full moon, has neither lack nor excess. It is this mind which is enlightened itself; the light of one's own mind flashes through the past and shines through the present.
The mind is like the ocean water, the body is like the waves. As there are no waves without water and no water without waves, water and waves are not separate, motion and stillness are not different.
Now Zazen is going right into the ocean of enlightenment, thus manifesting the body of all buddhas. The innate inconceivably clear mind is suddenly revealed and the original light finally shines everywhere.
Those who wish to illumine the mind should give up various mixed-up knowledge and interpretation, cast away both conventional and buddhist principles, cut off all delusive sentiments, and manifest the one truly real mind - the clouds of illusion clear up, the mind moon shines anew.
The Buddha said, "Learning and thinking are like being outside the door; sitting in meditation is returning home to sit in peace." How true this is! While learning and thinking, views have not stopped and the mind is still stuck - that is why it is like being outside the door. But in this sitting meditation, Zazen, everything is at rest, and you penetrate everywhere - thus it is like returning home to sit in peace.
An ancient said, "When confusion ceases, tranquility comes; when tranquility comes, wisdom appears, and when wisdom appears, reality is seen."