Thanks, that has cleared it up. Although I'm confused because in Zen one can become enlightened at any moment, throgh zazen or koan practice, yet here you are saying it's a very very gradual process. So if one is "enlightened" such as Suzuki Roshi, in actual fact here you'd say he was merely a non returner?
"The original heart/mind shines like pure, clear water with the sweetest taste. But if the heart is pure, is our practice over? No, we must not cling even to this purity. We must go beyond all duality, all concepts, all bad, all good, all pure, all impure. We must go beyond self and nonself, beyond birth and death. When we see with the eye of wisdom, we know that the true Buddha is timeless, unborn, unrelated to any body, any history, any image. Buddha is the ground of all being, the realization of the truth of the unmoving mind.” Ajahn Chah