The tradition is not part of the Hinayana ("Lesser Vehicle") schools that Mahayana ("Great Vehicle") Buddhism sought to ridicule, such as the Sarvastivada, which were successfully wiped out and replaced by Hindu-influenced Mahayana. But as the oldest tradition closest to the defunct schools, explaining the deep philosophy and facts of this major Buddhist lineage.
The Northern School/Southern School distinction is also misleading. Hinduism went everywhere Buddhism, but in most places did not catch on, except as a major unnamed influenced in Mahayana.
Theravada began in India, spread to the Indian island of Sri Lanka (the southern tip of the subcontinent), and spread east to encompass pocket from Israel (a metropolitan place far in the west) to Vietnam (far in the east). Two empires in particular helped it spread, Asoka's empire of Greater India (Maha Bharat) and the Khmer empire now limited to Cambodia). Jesus (St. Issa) was influenced by Theravada and Mahayana (see Holger Kersten) and his teaching seems to serve as the basis for Christianity.
The Three Wise Men (or Kings) from the East were Buddhist monks in search of a tulku (reincarnating lama). This is not to say that this actually happened, just to say that it became part of the mythology around Jesus ("Zeus' son" according to St. Constantine at the Council of Nicea). The search for the Messiah seems to be the search for the Buddha-to-come Maitreya. As Kersten's scholarship reveals, there was a well established Jewish settlement (trading outpost) in Kashmir, India to which Jesus traveled with a Silk Route trading caravan.
The countless similarities between Buddhism and Christianity (even as it was reshaped and made almost unrecognizable by the Greek and Roman empires) in both the Greek Orthodox and European Catholic monastic traditions is no accident at all. But what Christianity teaches is far more a Chinese-style imperial Mahayana, a covert kind of Hindu conception rooting it back to Sumerian, Mesopotamian, and Egyptian astrotheologies.
fed to us: Astrotheologically, it is the same old Sun and star worship.
Theravada differs from most religion in that it attempts to uphold the message of the historical Buddha. Mahayana, by contrast, takes the old Hindu (and Vedic civilization) pantheon and rebrands it as countless buddhas. The gods of old were extraterrestrials from heaven with their own back stories. Mahayana kept these gods, but by calling them Buddha this and Bodhisattva that, all the same worship continued.
The historical Buddha brought something altogether new to the practice of spirituality. A reliance on oneself as a lamp and an island guided by the Enlightened One (while he lived and taught and established a dispensation), the Teaching of Enlightenment (the Dharma), and those who had successfully followed that Path and confirmed its efficacy (the noble Sangha).
While Mahayana is much more about devotion and looking outside oneself for worldly success and a heavenly rebirth -- just like most of the religions of old -- with an emphasis on the wonderful Divine Feminine (Mother Goddess) Kwan Yin (Christianity's Virg Yin), Theravada kept to a more focused aim: enlightenment in this very life and final nirvana within seven lives.
The first stage of enlightenment (stream entry) used to be the focus of both traditions. But Mahayana philosophically veered far from it to a sort of messianic complex (everyone is a bodhisattva, and bodhisattva vows are the only acceptable career for new Buddhists to take, for anything else would be "selfish." And all the Buddha's original disciples, the theras (elders) who were arhats (enlightened in this very life) must, by implication, be "selfish dummies" relying on "expedient means."
And the Buddha himself could not have really entered final nirvana (parinirvana) because that could be interpreted as "selfish." The bickering between modern Mahayana and "Hinayana" apologists can get absurd. There was no division in ancient times when Mahayana ideals were closer to the root tradition.
But Hinduism (which was really Vedic Brahmanism before Adi Shankara came along long after the Buddha to create it) was always hostile to the Buddha's liberating message and human potential. It always preferred a heaven-centric philosophy, relying on Great Brahma, supplicating devas (light beings from space and nature), and centering around a hierarchical-patriarchal (often quite sexist) temple establishment.
What does Theravada offer instead? Imperfectly it tries to retain the Buddha's original message. Asked if he were a god (extraterrestrial deva), a yakkha (powerful extraterrestrial being), or what, he answered simply, "I am awake" (buddha simply meaning "Awakened One"). He had not relied on the gods or come as a heavenly "savior."
Starting here and rooted here on the human plane, he found the Path to freedom from all suffering. This Path is not limited to humans but also is the way for devas, brahmas, and all beings. Other beings generally do not have the opportunity to strive all the way to the final in the present life, but all would benefit along the way.
Humans and lower devas (within the Sense Sphere) are the ones the Buddha focused on teaching because they are capable in this very life of gaining absorption (purifying serenity) and liberating insight by following the guidance of the Three Gems (Buddha, Dharma, and Sangha). Mahayana has made each of these three something else:
The "Buddha" has become countless buddhas, any king or philosopher or messiah; the Dharma has become 80,000+ teachings (mixed with Confucianism, Taoism, and even the Brahmanism the Buddha rejected); the Sangha has become any Buddhist "community." Is it any wonder Mahayana practice looks very little like the historical Buddha's dispensation?
Mahayana is wonderful. It is rich and cultural. It is philosophical and exalted. And it has the best art.
But if one would seek enlightenment (understanding it to be a very unselfish thing to free oneself from greed, hatred, and delusion and help and inspire others to do the same) in this life, one would certainly investigate Theravada and the unimaginable riches of the Pali Canon.
Pali is the exclusively-Buddhist language. It is closest to the Prakrit or Magadhi language the historical Buddha spoke, while the brahmin priests around him had their secretive Sanskrit for mantras and aloof scholarship, which served a role quite like Latin in the Catholic Church.
Zen has been a push to return Mahayana Buddhism to its essentials -- just sitting to reach satori (an epiphany). But most Americans misunderstand what "Zen" means and take it to mean a free-for-all without rules or guiding ideals when it is anything but that in Asia.
It is therefore no wonder that Zen Buddhism, according to Wisdom Quarterly, the most popular type of Buddhism in the West and in America in particular. (See the myth-shattering work of UCLA's Prof. Buswell a former Zen monk in Korea who also studied Theravada monasticism).
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