As Buddhism has been characterized as the least dogmatic religion, so Zen can be characterized as the least dogmatic practice of Buddhism. It’s structures are simple, its accomplishments vast, and over the centuries its adepts many.
Nevertheless, Zen is a religion in that confidence in the complete liberation of Buddha Shakyamuni is necessary for one’s own complete liberation. If one has no confidence that any human being has or can achieve complete freedom, then what is the point of trying to achieve such freedom? In addition, the practitioner of Zen must exert effort with determination toward the goal of liberation and have persistence despite obstacles, or the lack of complete freedom.
The two main schools of Zen are called Soto and Rinzai which differ in their emphasis on shikatanza (sitting with confidence in the presence of a Zen master) and Koan (exhaustion of mental constructs by means of a mental construct). Both are designed to lead to one-pointed rest in non-dual awareness, whether one is sitting still or moving about in activity. What does this mean?
According to the Buddha, the dualities--the polarity-- we experience is not real--not really there. (In fact, the Buddha once characterized our experience as "insane"--one might say, "bi-polar.") Nevertheless, experiential non-duality is not about one tradition or another, one practice or another, let alone one tradition or practice over another. Those dualities, likewise, are not really there.
However, most of us most of the time experience a tension, the opposition/ conflicts, as real, and we must remain true to our experience, authentic, as is said, and work with that. Regardless of experiencing non-duality (which is not really an experience in the conventional sense of experience) and knowing that that is Reality, we must continue to respond, to the best of our ability, based on our experience of duality, "illusory" as it may be. And that is okay--we have to relax about that. We cannot wave it away, simply by telling ourselves "it’s not there; it’s an illusion." Because if we do not act authentically on the basis of our experience, which is all we truly can rely on, then how can we ever hope to realize non-duality moment-to-moment, which is another way of saying "permanently"? If we do not remain true to our experience in this moment, then how can we hope to remain in-the-moment non-dually. Most of us do not have the habit of remaining in the moment.
This is the classic way of teaching on the reality of karma--of our experience of duality--and that we must act accordingly, because you cannot escape karma by ignoring it, by being inauthentic to it. Without authenticity to one’s experience--or integrity--there is no possibility of liberation from dualistic, experiential karma--from the dualism that is experienced by all of us. In this we are no different from each other and all beings.
If we ignore karma--if we ignore the practice of virtue--regardless of our experience of non-duality--then we are not remaining true to experience. Those who teach non-duality and yet practice non-virtue are unwittingly teaching that karma can be ignored, that it is okay to ignore duality and the authenticity, integrity of experience--which is all we have to work with as beings--as well as the teachings of all the virtue traditions (that teach the truth of karma/virtue) as the only basis for true wisdom (moment-to-moment realization of non-duality). Even when we appear not to be acting (like sitting in meditation)--we are acting--albeit virtuously. Non duality is not affected by our actions, good or bad--virtuous or non-virtuous, but we, as beings in duality, as beings not remaining in-the-moment non-dually, are. We cannot escape unless we remain--cannot get out unless we stay.
The reason, it is said, that most of us do not become completely free of karma/duality, having glimpsed, experientially, non-duality, is precisely because of our habits—strong karmic habits--of not remaining true to our experience in the moment--of not remaining in the moment--but always instead running after the next moment and grasping on to the last or the long ago moment--even the momentary non-dual experience (which by this point has become an experience).
The practices developed are for working toward that non-duality, and then, what do we do for an encore? Well, what we have been doing: "dance with the one that brung ya!" Naturally, one is then drawn to deepen the practice of non-duality and to glimpse reality as it really is, moment to moment, continuously. But that takes time. One must be patient. And remain relaxed and avoid the most common of obstacles on the path ever unwinding (unfolding): the attempt to re-create the non-dual experience or any experience for that matter.
This moment-to-moment approach is the fundamental approach of what is called Zen. Since non-duality can be realized by anyone anywhere at any moment, it follows that one could concentrate on the moment, the present, as much as possible, moment to moment.
A great variety of practices have been developed to that end--but that end is not an end but a means, and then it is said, the final realization is realized: the means to the end is the end and the end of the means is the end of the end. Means and ends also are fundamentally dualistic, so even that dualism--the dualism of practice toward a goal--must be realized as illusory, as illusory, that is, as good and bad, and all the other dualities we experience.
Whether through the practice of sitting, or doing whatever we are doing, we must maintain integrity to our experience as it is. The Path of Escape is the practice of not Escaping, that is to say, relax in the moment and not try to escape the moment, to escape our thoughts/feelings, or to escape the results of our words and actions.
For more information:
Recommended reading: The Three Pillars of Zen, by Roshi Philip Kapleau