The great death, oneness, enlightenment, total acceptance of reality beyond good and evil - this is a necessary step in Zen or any other profound spiritual practice. But although this may be ultimate, it is only a step. Zen calls it 'the great death' for a good reason. It is a kind of 'death.' It requires a complete letting go, a complete relinquishment, in trust, of everything that one has identified as one's life.
To be truly alive, as Zen sees it, one has to die - to let go of life. But until we are physically dead we can't remain dead. We have to be alive. We can't remain in the darkness and purity of beyond-good-and-evil. We have to arrive in the daylight of this physical, limited world of distinctions and moral choices. Difficult though it may be, there is no escape and no alternative. And yet we celebrate. Having died the great death, we know what a miracle it is to be alive, and how strange and marvelous it is - even with its difficult and sad challenges, which are themselves miraculous."
Norman Fischer "The Problem of Evil" Shambhala Sun, May 2015. http://www.lionsroar.com/category/shambhala-sun/
The 'great death' also appears in other wisdom traditions:
“At three o’clock, Jesus cried out in a loud voice, ‘Eloi, Eloi, lema sabachthani?’ which is translated, ‘My God, my God, why have you forsaken me?’” (Mark 15:34; Matthew 27:46)