The word "enlightenment" in a Buddhist context has been used so frequently and in so many ways, many people may not realize that this use of the word began fairly recently, and has a complex cultural and literary history.
Though 19th century translators of Buddhist texts sometimes used the word "enlightenment" to refer to Gautama's moment of spiritual awakening on seeing the morning star, the first time a large number of general English readers saw the word used as a spiritual term was with the publication Essays on Zen Buddhism First Series by D.T. Suzuki in the 1930s. Before that time the word referred to the 18th century rationalist movement in Europe that strove to understand the world using logic and reason.
D.T. Suzuki used the word "enlightenment" to translate the Japanese term satori¸ and his recounting of the enlightenment stories from the Zen koan literature made quite a splash among intellectual elites at the time. From that time forward, the idea of a sudden transformative spiritual experience became embedded in Western cultural imagination. It is worth nothing that D.T. Suzuki paid relatively little attention in his writings to the Buddhist practices of precepts, mindfulness, meditation, and the monastic life.
The best-selling books of Alan Watts in the 1950s, and Philip Kapleau's The Three Pillars of Zen in the 1960s, filled in some of D.T. Suzuki's omissions (Kapleau's book had good instruction about how to meditate, for example). But it was not until the arrival of Asian teachers in the late 1960s, that students began to understand that Buddhism was about much more than a single epiphany; it was a lifelong path of spiritual development which included both sudden and gradual transformations.
It was Shunryu Suzuki (not D.T. Suzuki), who said in the 1960s, when asked directly about satori, "Satori is not the part of Zen that needs to be stressed." (This was quoted in the introduction to the paperback edition of Zen Mind, Beginner's Mind). In other words, he did not deny the reality or importance of satori; he just pointed out that satori, when separated from rest of Buddhist practice, has a tendency to devolve into just another object of desire, something the ego wants for itself.
"Satori" is the Japanese reading of the Chinese character "wu," which is in turn a Chinese translation of the Sanskrit "bodhi," which does indeed mean spiritual insight or awakening. We see this root term in words such as "bodhisattva" (literally enlightenment-being) or "bodhicitta" (the thought of enlightenment). Some Buddhist scholars (Edward Conze, for example) have felt that the Zen emphasis on satori as the sine qua non of Buddhist experience is somewhat outside the mainstream of Buddhist tradition. The Buddha himself taught an eight-fold path with many facets, all of them important. The Tibetan and Vipassana approaches each have detailed descriptions of the gradual stages of spiritual development. Even within Zen, there were various schools and approaches; not all of them emphasized satori as primary.
During the psychedelic revolution of the 1960s the sudden alteration of consciousness brought on by LSD and other drugs dovetailed neatly into the satori stories of Zen. Many veterans of psychedelics sought out Buddhist teachers to see if meditation could reproduce those altered states. Many Buddhist teachers and writers worked to counteract that view. That may have been the context of Shunyru Suzuki's remark about satori. Lama Anagarika Govinda, a German-born Buddhist teacher popular at the time, likened the psychedelic experience to a deep rut in the center of a wide road. Once you have carved that rut, he said, all your other spiritual experiences tend to roll down into it.
In the 1960s book Conversations Christian and Buddhist by Catholic priest Aelred Graham, he recounts the time Yamada Mumon Roshi, an eminent Japanese Zen Master at the time, took LSD. Mumon Roshi's comment about the experience was, "This is form is emptiness, but this is not emptiness is form."
Shunryu Suzuki had his own teaching on this point. He said, "'Form is emptiness' is relatively easy to understand; 'emptiness is form' takes a lifetime."
It will be interesting to see how the next generation of Buddhist teachers and practitioners deal with the cultural history (and baggage) of the word "enlightenment." Maybe they will bypass it; maybe they will change it. I have a feeling that whatever they do they will come up with their own rather different understanding (and possibly mis-understanding) of this deep matter.
I myself have had forty years to ponder Shunryu Suzuki's comment, "Satori is not the part of Zen that needs to be stressed." As I see it, it is a little like standing on a hilltop with a good friend at dawn, watching the sun rise and saying, "Look, the sun is rising." It's not really necessary to say so. It is obvious; that is why you are there. It's best to just stick with it, watch closely and see what happens.