Things have never declared themselves empty, nor have they declared
themselves form; and they have not declared themselves right, wrong,
defiled or pure. Nor is there a mind that binds and fetters people.
It is just because...
ZAZEN MEDITATION GUIDE - Chapter 16. Zazen vs Reading Buddhist Scriptures and Zen Masters' Sayings
As you might know, If there were not the Supreme Enlightenment of the Buddha and his Teachings in the Buddhist sutras handed down to the present, there would not be Buddhism or Zen or zazen at all. It can be said dhyana (in Sanskrit) or zazen (in Japanese) is the method the Buddha practiced at least in six years long before He attained Enlightenment when He saw the morning star.
If all of the sutras are the description of the Buddha's Enlightenment then dhyana practice is the means to prove the experience of that. The same way of speaking can be applied to Zen masters' records and zazen.
Zen masters' records are the description of their experience of enlightenment and zazen practice is the means to prove it. The Enlightenment of the Buddha and experience of awakening of Zen masters are the same in quality. If there is anything different, it will be the difference in the degrees of depth in experiences, and the way the Zen masters used to express their experiences and teachings.
The difference in the forms of expression is necessary, because if not, it will not be Reality. Truth cannot be a repetition of the same words all the time. And the Zen masters have shown their genius in their particular way of expression.
On the other hand, when a student practices Zen under the direct guide of a Zen teacher, especially when he is sitting in zazen, he is not supposed to remember any words, even though they are the words of the Buddha or of any Zen master he learned or knew. This is because he is doing the same thing the Buddha did more than 2,500 years ago.
He is discovering the truth for himself and by himself, and what he can find will be his own and not a thing he borrows from the Buddha or Zen masters.
More than that, he is becoming himself as a Buddha. This is the very thing the Buddha wants every being to do. This is called the Equality and Freedom in Buddhism and it makes Buddhism unique in this characteristic among the world religions.
However, after attaining kensho (seeing into one's own nature or Buddha-nature), the Zen student has to keep not only practicing zazen but also studying the Scriptures, as he would be advised, to develop his own experience until to the Perfect One..
When a monk asked a Zen master: "What is the difference between the meaning of Zen patriarchs' teachings and that of Buddhist sutras?" The master replied: "When it is cold, hens go to trees and ducks go to the lake."