THE JAPANESE TERM “Zen” is an abbreviation of the term, zenna, that is a transliteration of Chinese Mandarin ch’anna, that is a transliteration of Sanskrit dhyanna and/or Pali jhana, and all terms describe a consistent form of meditation. But meditation is not really the “essence” or primary point. The essence is the core direct experience of true home/true nature, and this is not exclusive to Siddhartha, and can be experienced outside Buddhism and is accessible to anyone. It is a dimension of human experience. As Siddhartha reportedly said, this is a direct experience of nature/essence that cannot be taught. Zen Buddhism has provided strong advocacy for this directive, but with up and down cycles of stagnation and misdirection and reformation aspiring to return to this primary
In Zen sects of Buddhism, there was a deepening shift toward Mahayana doctrine that kept turning “Zen Buddhism” toward either remaining or returning [reforming] practice to the core direct experience. Zen was/is “the study of self” rather than being sitting [za, J.] per se, with meditation being useful but not essential for awakening to “true nature/true self/true home.” Sixth Chinese Ch’an patriarch Hui-neng represents this sense well in accounts that describe and value Hui-neng as an illiterate woodcutter and experiencing sudden awakening upon hearing a phrase from the Diamond Sutra being recited by a monk in a local marketplace, and with transmission of the core essence or primary point be acknowledged by the Fifth patriarch without ordination (that would likely not have even allowed presence in the meditation hall and had kept him a cook).
Zen or whatever term is applied aspires to address the human dilemma as caused by the ignorance of true nature. It aspires to cut through the conceptualization. And it likely appears more in Zen and sustains because of a Zen orientation than it might in more spontaneous experience. However, Zen practice and related meditation practices both monastic and lay can become blindly arrogant as well as intentionally arrogant and get caught up in practice rather than essence.
We do not really know the historical Siddhartha. We do not explicitly know when or where he was born or when and how he died. While the continuation of his teaching by his followers is described, we have no written words from him, and his “sayings” only appearing in written form after being passed down by zealots centuries later. And those documents have mythical and magical qualities that do not fit well with Siddhartha’s core realization. As with most derivative practices, those retellings may or may not imagine, for example, supernatural events such as possible virgin birth [i.e., his mother having a dream of being pierced by an elephant tusk and then birthing a child with myriad markings suggesting greatness].
We imagine Siddhartha leaving home and creating something exclusive that would come to be termed “Buddhism.” There is no acknowledgement of many spiritual and philosophical practices under a broad canopy of Hinduism and other practices such as Jainism, and many strong personalities to which Siddhartha would have been exposed and a religious practice he had been indoctrinated in and against which he was reacting. There was also a cultural context of widespread illiteracy (even Siddhartha may have been illiterate), and an absence of cultural comfort that requires nearly full-time effort to exist and a broad spiritual climate that favored magical beliefs. This is important because core elements of meditation and ideas such as the ineffable and phenomenon being “one” and attachment to either and the inability to experience integration of these two dimensions of being as root suffering were not new.
In his lifetime, Siddhartha was actualizing aspects of existence and transcendence that were clearly described in the Upanishads that predate Buddhism and that were being discussed broadly. There are philosophical aspects of, for example, Hinduism (as expressed in some of the Upanishads) that mirror ontological aspects found in Buddhism (as expressed in Mahayana documents such as the Diamond Sutra). Further, beliefs that contradict what Siddhartha had intuitively experienced such as reincarnation were either transposed onto his “Buddhism” OR he continued to describe his experience in such terms as recounted in an eventual written record [e.g., in his process of awakening, first perceiving 100,000 previous births and eventually leading to the cessation of his suffering due to his rebirth being destroyed and “no more re-becoming” [Majjhima Nikaya 26.2, in H.W. Schumann, The Historical Buddha, 2004 Ed., p.54].
Because of our distance from a historical Siddhartha, it is possible that Siddhartha might have described an ontology that did carry forward pre-existing religious concepts such as karma and reincarnation that carry the individual soul forward after death. Such an orientation is clearly expressed in volume after volume. For example, there are statements by respected contemporary Buddhist teachers such as (1) nirvana will be automatically attained in your eighth reincarnation as a monk if not before, and (2) the reason for so many people in the modern world is the result of killing and eating so many animals (causing so much suffering) that the animals were “elevated” and reincarnated as humans.
Depending on one’s Buddhist lineage, there were perhaps thirty or so primary transmitters after Siddhartha in Indian, followed by perhaps nearly thirty primary transmitters in China, and then splaying out into twenty generations each or so in Japan and Korea and SE Asia. And in this process, there were the cultural influences of, for example, Taoism in China and shamanic practices and folk religions and varying conditions of existence.
The core element that distinguished Siddhartha from many other spiritual practices of that historical moment was the idea of the necessity of a sudden primary, direct experience of true self or true home that contradicts the nearly universal spiritual idea of an eternal individual soul or spirit. Meditation had long existed, but the primary effort of previous practices had been an effort to link self with a theological being or absolute reality rather than stepping beyond a psychological self. With an orientation in China that would become Ch’an Buddhism, one early name translated as “Buddha Soul Sect” which implied a sense of all as buddha soul [somewhat like the Upanishad idea of atman—a “seed” that dissolves back into Brahman or absolute reality at death, with Brahman actualizing atman more as an inseparable expression like a wave in the ocean].