The Zen path leads, through the Gateless Barrier, straight to non-duality. Here, subject and object merge into an indivisible, seamless whole; there is no separation between me and the world. Boundaries dissolve, and I become the entire universe--and it becomes me. Ego drops off completely, what Dogen means when he says, "Enlightenment is intimacy with all things," and "to study the self is to lose the self." This is the primary purpose of koan study.
A common explanation of why we suffer is because we separate ourselves from the world. There's us on the one hand, and everyone and everything else on the other. We are subjects while the rest of the world, as outsiders to our inner experiences, are mere objects, usually standing in opposition to our goals. This kind of thinking turns the world into an obstacle to be overcome. On a psychological level, our lives slip into quiet antagonism as we try to squeeze our desires out of an obstinate, uncooperative world. This leads to feelings of anger, fear, frustration, alienation, and loneliness.
But I think there's an even subtler form of dualism at work here, one that is commonly overlooked in our conversations regarding non-duality.
Not only do we view the world as "other," but we see our very bodies and actions as "others" too. All too commonly, we treat our bodies as vehicles to transport our minds around, organic machines that obey our commands, which usually consist of gratifying one desire after another. Sure we experience pleasure from our senses, but as a distinct "I" who is separate from the sensation. This creates "the act of sensing" or "experiencing," rather than simply being the experience. We are housed inside of our heads, mere minds divorced from our bodies--the Cartesian mind/body split run amok.
Part of this disassociation (I use the term here, not in a clinical sense, but as a more emphatic form of differentiation) stems from our imagined separation from our actions. When we run, we imagine that there is some "us" inside our bodies commanding our bodies to run, or that running is somehow separate from our bodies! The same goes for eating, jumping, listening, seeing, etc.
But this is not the case at all. There is no "I" outside of this field of experience. There is only eating, jumping, listening. There's no need for this middle man called "I" to constantly "experience" our actions. To quote the Master Lin Chi, that's "putting a head on top of your own head."
Part of this confusion is linguistic. Wittgenstein points out that language limits our world, and unless we pay close attention to language, we can very easily get hijacked by it. For example, when I say "in my head," "in" means something different here than "in the house." But we confuse the two usages and think they're the same. This creates the sense of some me "inside" of my body. But where is it? Why can't I find it "inside" me?
Another grave linguistic misconception is how we cut up reality in terms of subjects separate from verbs, as if there could ever be a subject that wasn't doing something. This is an even subtler manifestation of the classic subject/object split (i.e., imagining a subject without an object). Talk about the tail wagging the dog!
The end result is a false view of the world that causes us and others pain and suffering.
One alternative is to stop thinking of ourselves as static nouns, but rather as verbs. If we truly internalize the Buddha's teaching of impermanence, we will see that change doesn't happen to us, it is us. We are the flux and flow or the universe, and in that sense we resemble verbs much more than we do nouns. For there's no part of ourselves that we can ever pin down--the moment you think you've caught some emotion or experience, it's gone. Transformed into something else. But the change isn't separate from us, it is us.
To resist is to cling, to suffer; to open ourselves is to find freedom.
Once we accept the changing, impermanent nature of our existence--in effect, obliterating the myth of a fixed self looking out at the world--we can then reclaim our bodies and our actions. And thus ourselves as change itself.
This is what the old Zen masters mean by "Just wash the dishes," and the purpose of rituals in Zen practice. "To be intimate with," as Dogen might say. After a time, there is no distinction between you and the act of washing the dishes or bowing or chanting, for there is only washing the dishes, bowing, chanting. This is everyday Samadhi, an experience we commonly overlook. Most of the time we would call it, "losing ourselves." Like when you get sucked into a great movie, a beautiful song, a game of basketball. The entire world disappears, including our sense of ourselves. Lin Chi's second head drops off--you, watching, and the movie, all collapse. Just this moment, that's all there is.
And you come to realize that beneath all our concepts, delusions, and dualisms, that's all there ever was.