The word nirvana actually connotes death, as I understand that it can be translated as “extinguishing,” as in the blowing out of a candle. Some modern people find reassurance in the concept of reincarnation, taking it to mean that we don’t really “die” at all, but merely come back as some other person or life form. However, back at the time of the Buddha, people dreaded the concept of constantly returning to existence over and over again, only to be once again subject to suffering and disease, old age, and death. People sought an escape from the cycle of samsara and during the Buddha’s lifetime, many spiritual teachers were proposing various practices and methods to escape or avoid this endless cycle. Nirvana to them was the ultimate death, the true death, the state of no more becoming.
This is the context in which the Buddha’s teachings were first presented. The passing away of a Buddha is called the parinirvana, as the Buddha then leaves the cycle of samsara and does not return again. The flame is extinguished.
It’s also interesting to note as an aside that this concept of the extinguishing of a flame also had a subversive double meaning. The Brahmans at the time taught that the responsibility of each householder was to constantly keep three flames burning in the home at all times (don’t ask me why - I’ve forgotten), and by advocating the “blowing out of the flame,” the Buddha was also symbolically rejecting the teachings of the Brahmans. He even went so far as calling the “three poisons” – greed, hate, and delusion - the “three flames” that must be extinguished first before the ultimate extinguishment (nirvana), which was an even more explicit and confrontational rejection of the Brahmans. All of this is just an aside, but I find it interesting to note how the Buddha was willing to explicitly reject the teachings of others.
Anyway, nirvana is escape from the cycle of samsara, and parinirvana is the final death with no more becoming. This is why early Buddhists texts and some Theravedan teachings still talk about classes of Buddhist practioners, including, stream-enterers (those just starting in this lifetime), thrice-returners (those who’ve entered the stream in a previous life, but still have three more lifetimes to go to further purify themselves before entering nirvana), and arhats or saint-like persons who are free from greed, hate, and delusion due to the actions of their previous lives and current practices, and who will enter into nirvana upon their passing.
After about 500 years or 14 generations of teacher-to-student transmission, this school of thought was overturned by the Patriarch Najaruna, who changed the emphasis from the arhat seeking his own nirvana to that of the bodhisattva who seeks instead to free all other sentient beings from samsara. This was the first great division of Buddhism into the so-called Mahayana, or “Greater Vehicle” and the traditional Theravedan schools, and to support the Mahayana views, sutras such as The Diamond Sutra were emphasized (or possibly even made up at the time).
It was the Mahayana teachings that were transmitted to China and encountered Daoism, and then this Daoist-influenced Mahayana Buddhism became Japanese Zen. The teachings were being transmitted from Japan to the West by teachers like Sunryo Suzuki of the San Francisco Zen Center and Soyu Matsuoka, my teacher’s late teacher. As I understand it, these teachings do not emphasize future lives so much as this very life here and now, and nirvana, or the death of the ego-self, usually referred to as satori by the Japanese teachers, can be experienced right now, in this very life time. Even more specifically, the Soto Zen way is that we can experience body-and-mind falling away and lose the ego-self through the practice of shikantaza, or “just sitting” – zazen that seeks no ultimate goal but is just the natural way of abiding.
Sitting in zazen and experiencing the falling away of body-and-mind (I insist of hyphenating it to remind myself that it is not two separate things, but one, that falls away) is essentially the same experience as the extinguishing of the flame of existence. It is the at least temporary death of the self, and a step outside of the cycle of samsara. It is no small thing. This is why Dogen said that practice (shikantaza) and enlightenment are one – losing one’s self during zazen is to directly experience the self as the temporary aggregation of the five skandhas, the effect that comes from the coming together of bodily form, sensation, thought, samskara, and consciousness. When thinking stops, or is at least sufficiently ignored, there is nothing holding the aggregation together, and the “self” disappears (body-and-mind falls away). This is what I understand to be “dying on the cushion.”
In my own experience, and in my studies of Zen, the constructed ego-self does not want to die, even if temporarily. We obsessively cling to the illusion of “being,” and the mind creates all kinds of obstacles and distractions to keep us engaged in the process of thinking and thereby keeping the illusion going. This is what the Buddha experienced as the manifestations of Mara trying to keep him from continuing his mediation by first distracting him with pleasurable fantasies and then with terrifying images and doubting thoughts. The mind is very clever - in fact sometimes I joke that it is exactly as clever as you are (since it is you) - and it can manifest all sorts of thoughts, sensations, ideas, doubts, cravings, fantasies, and so on to keep us engaged in thinking and not letting go of our thoughts.
This is where a teacher can come in. Ultimately, there is nothing to teach, but a teacher can encourage us to keep practicing zazen and help us dispel the concepts that the mind creates as barriers to letting go of thinking. A teacher encourages us to practice shikantaza (just sitting) and experience for ourselves the dropping away of body-and-mind.