(an excerpt from Dogen's Shobogenzo)

a.txt

Question 10: Some have said: “Do not concern yourself about birth-and-death.
There is a way to promptly rid yourself of birth-and-death. It is by grasping
the reason for the eternal immutability of the ‘mind-nature.’ The gist of it is
this: although once the body is born it proceeds inevitably to death, the
mind-nature never perishes. Once you can realize that the mind-nature, which
does not transmigrate in birth-and-death, exists in your own body, you make it
your fundamental nature. Hence the body, being only a temporary form, dies here
and is reborn there without end, yet the mind is immutable, unchanging
throughout past, present, and future. To know this is to be free from
birth-and-death. By realizing this truth, you put a final end to the
transmigratory cycle in which you have been turning. When your body dies, you
enter the ocean of the original nature.48 When you return to your origin in
this ocean, you become endowed with the wondrous virtue of the
Buddha-patriarchs. But even if you are able to grasp this in your present life,
because your present physical existence embodies erroneous karma from prior
lives, you are not the same as the sages.  “Those who fail to grasp this truth
are destined to turn forever in the cycle of birth-and-death. What is
necessary, then, is simply to know without delay the meaning of the
mind-nature’s immutability. What can you expect to gain from idling your entire
life away in purposeless sitting?” What do you think of this statement? Is it
essentially in accord with the Way of the Buddhas and patriarchs?

Answer 10: You have just expounded the view of the Senika heresy. It is
certainly not the Buddha Dharma.  According to this heresy, there is in the
body a spiritual intelligence. As occasions arise this intelligence readily
discriminates likes and dislikes and pros and cons, feels pain and irritation,
and experiences suffering and pleasure—it is all owing to this spiritual
intelligence. But when the body perishes, this spiritual intelligence separates
from the body and is reborn in another place.  While it seems to perish here,
it has life elsewhere, and thus is immutable and imperishable. Such is the
standpoint of the Senika heresy.

But to learn this view and try to pass it off as the Buddha Dharma is more
foolish than clutching a piece of broken roof tile supposing it to be a golden
jewel. Nothing could compare with such a foolish, lamentable delusion. Huichung
of the T’ang dynasty warned strongly against it.50 Is it not senseless to take
this false view—that the mind abides and the form perishes—and equate it to the
wondrous Dharma of the Buddhas; to think, while thus creating the fundamental
cause of birth-and-death, that you are freed from birth-and-death?  How
deplorable! Just know it for a false, non-Buddhist view, and do not lend an ear
to it.

I am compelled by the nature of the matter, and more by a sense of compassion,
to try to deliver you from this false view. You must know that the Buddha
Dharma preaches as a matter of course that body and mind are one and the same,
that the essence and the form are not two. This is understood both in India and
in China, so there can be no doubt about it. Need I add that the Buddhist
doctrine of immutability teaches that all things are immutable, without any
differentiation between body and mind. The Buddhist teaching of mutability
states that all things are mutable, without any differentiation between essence
and form.51 In view of this, how can anyone state that the body perishes and
the mind abides? It would be contrary to the true Dharma.

Beyond this, you must also come to fully realize that birth-and-death is in and
of itself nirvana. Buddhism never speaks of nirvana apart from birthand-death.
Indeed, when someone thinks that the mind, apart from the body, is immutable,
not only does he mistake it for the Buddha-wisdom, which is free from
birth-and-death, but the very mind that makes such a discrimination is not
immutable, is in fact even then turning in birth-and-death. A hopeless
situation, is it not?

You should ponder this deeply: since the Buddha Dharma has always maintained
the oneness of body and mind, why, if the body is born and perishes, would the
mind alone, separated from the body, not be born and die as well? If at one
time body and mind were one, and at another time not one, the preachings of the
Buddha would be empty and untrue. Moreover, in thinking that birth-and-death is
something we should turn from, you make the mistake of rejecting the Buddha
Dharma itself.52 You must guard against such thinking.  Understand that what
Buddhists call the Buddhist doctrine of the mindnature, the great and universal
aspect encompassing all phenomena, embraces the entire universe, without
differentiating between essence and form, or concerning itself with birth or
death.53 There is nothing—enlightenment and nirvana included—that is not the
mind-nature. All dharmas—the “myriad forms dense and close” of the universe—are
alike in being this one Mind. All are included without exception. All those
dharmas, which serve as “gates” or entrances to the Way, are the same one Mind.
For a Buddhist to preach that there is no disparity between these dharma-gates
indicates that he understands the mind-nature.

In this one Dharma [one Mind], how could there be any differentiation between
body and mind, any separation of birth-and-death and nirvana? We are all
originally children of the Buddha, we should not listen to madmen who spout
non-Buddhist views.