The past couple of Monday nights, we've been talking about buddha-nature, using the koan of Jōshu's Mu as a starting point. Buddha-nature is usually understood as the potential we all have to attain the truth, or as something which we have inherently and which grows naturally day by day.
But no, that explanation wasn't good enough for Zen Master Dōgen. In his view, buddha-nature is neither a potential nor a natural attribute, but a state or condition of body-and-mind at a present moment. Therefore, he saw buddha-nature neither as something that we might realize in the future, nor as something that we have inherently in our body and mind. From this standpoint, Master Dōgen affirmed and at the same time denied the proposition “We all have buddha-nature.” But he also affirmed and at the same time denied the proposition “We all don’t have buddha-nature.”
At first sight, these views appear contradictory, but what Dōgen asserts is essentially that no sentient being is devoid of buddha-nature while at the same time no sentient being possesses a thing called "a buddha-nature." All sentient beings have buddha-nature through and through; that is, they are inseparable from buddha-nature, are completely possessed of buddha-nature, and indeed are buddha-nature.
Further, not only all sentient beings, but the whole earth with all of its mountains and rivers and the rest of the entire universe is nothing but buddha-nature. To look at mountains and rivers is to look at buddha-nature, and to see buddha-nature is to see the world without any taint of discriminatory judgement.
Buddha-nature, then, is the "cookie dough" from which our discriminating minds, like cookie cutters, form the various shapes and sizes that we come to think of as separate things, including our own selves. And since the nature of this "cookie dough," that is, the very fabric of existence, has no real substantiality and is nothing but potential, the ancient teachings of Shakyamuni Buddha begin to approximate the theories of modern physics that assert that sub-atomic particles, the building blocks of all matter, are just fields of probability - pure potential - and have no real form of themselves.
Cool, but so what? Or as a skeptic once asked the Indian Patriarch Nāgārjuna, “The most important thing in the world is the happiness of people. Why talk so meaninglessly about some ‘buddha-nature’? Who has seen such a thing?”
Nāgārjuna replied that buddha-nature is beyond happiness and unhappiness, and is beyond retribution, for it is unborn and undying. Since being alive is being born and dying, and since we are of the same nature and substance as that which is unborn and undying, were we to truly grasp this principal, we would lose all anxiety about life and death. As Yasutani taught, "You will then attain a steadfast mind and be happy in your daily life. Even though heaven and earth were turned upside down, you would have no fear. . . If you fall into poverty, live that way without grumbling - then your poverty will not be a burden to you. Likewise, if you are rich, live with your riches. All this is the functioning of buddha-nature."
"In short," Yasutani wrote, "buddha-nature has the quality of infinite adaptability."