It is difficult to think about enlightenment (S.;J., sambodhi, sambodai) as just the idea of perfect knowledge or awakening (from the verbal root budh, to awake, from which bodhi, an abstract noun, is formed). Perhaps somewhat better, enlightenment is closer to awakening to the essence of reality. But now we need to ask, how do we get there?
To awaken to such an essence is no easy task. There is nothing in our Western education that will help us since awakening is more of an intuitive process—certainly not an intellectual act. In Zen we get a little closer to what it means to awaken to the essence of reality. It is done suddenly in the sense of what was thoroughly hidden from the adept now issues forth all at once. Paradoxically, this revealed essence even when spoken of still remains ineffable. When the intellect attempts to conceive of it, it still remains unknowable. Language is not up to the task of getting us closer to enlightenment. Going from the concept of enlightenment to its actualization requires a leap of sorts.
For the one who is enlightened—who has made the leap—it was accomplished by dhyāna which I prefer to translate with the English word, intuition. Still, this doesn’t present us with the whole picture which explains the sudden awakening in which this essence issues forth from dark obscurity in the highest dhyāna. An exact how-do-you-do-it is too complex for most people. This may explain why Zen has turned into a religion of sitting.
Still, on almost every page of Zen sermons is an appeal to our intuitive abilities. This is especially evident in the rise of koans during the Song period. The structure of the koan is based upon essence 體 and function 用 (e.g., 外用 external manifestation). The goal is to pass through the gateless barrier 無門関, this strange barrier being function (or phenomena 事). Every koan has its gateless barrier (e.g., mu) that stops the intellect dead in its tracks. The only way to get past this barrier is for us to directly intuit our Buddha-nature or essence which is a sudden intuition.