The Eleusinian Mysteries.

I found this topic interesting; in so far as it is pre-Christian, and contains an interplay of a form of worship encapsulating; mythology, the ancient Mediterranean world as then known, man's place in it and even the seasons of nature.

The Eleusinian Mysteries were formal initiations held every year for the cult of Demeter and Persephone and were based at Eleusis in ancient Greece.

There are parallels to be drawn with the older Near East cults like Isis and Osiris in Egypt. It was a major festival during the Hellenic era, and later spread to Rome. What is quite remarkable is that the rites, ceremonies, and beliefs were kept secret and consistently preserved from antiquity. Mind you, once initiated, it was on pain of death that you divulged the secrets.

For the initiated, the rebirth of Persephone symbolized the eternity of life which flows from generation to generation, and they believed that they would have a reward in the afterlife.

The Mysteries themselves are related to a myth concerning Demeter, the goddess of agriculture and fertility. Demeter's daughter Persephone was assigned the task of painting all the flowers of the earth. Before completion, she was seized by Hades, the god of the underworld, who took her to his underworld kingdom. Distraught, Demeter searched high and low for her daughter. Because of her distress, and in an effort to coerce Zeus to allow the return of her daughter, she caused a terrible drought in which the people suffered and starved, depriving the gods of sacrifice and worship. As a result, Zeus relented and allowed Persephone to return to her mother, who initiated what was in fact the first spring.

However, it was a rule of the Fates that whoever consumed food or drink in the Underworld was doomed to spend eternity there.

Before Persephone was released to Hermes, who had been sent to retrieve her, Hades tricked her into eating pomegranate seeds, which forced her to return to the underworld for some months each year. She was obliged to remain with Hades for six or four months (one month per seed) and lived above ground with her mother for the rest of the year.

This left a long period of time when Demeter was unhappy due to Persephone's absence, neglecting to cultivate the earth. When Persephone returned to the surface, Demeter became joyful and cared for the earth again. Thus, Persephone is said to stay in Hades during winter and return in the spring of the year.

Persephone's rebirth became symbolic of the rebirth of all plant life and the symbol of eternity of life that flows from the generations that spring from each other.

One line of thought has been that the Mysteries were intended "to elevate man above the human sphere into the divine and to assure his redemption by making him a god and so conferring immortality upon him".

The Eleusinian Mysteries became pan-Hellenic, and pilgrims flocked from Greece and beyond to participate. Then around 300 BC, the state took over control of the Mysteries and they were controlled by two families, the Eumolpidae and the Kerykes. This led to a vast increase in the number of initiates.

The only requirements for membership were freedom from "blood guilt" meaning never having committed murder, and not being a "barbarian" (being unable to speak Greek). Men, women and even slaves were allowed initiation.

To participate in these mysteries one had to swear a vow of secrecy.

Four categories of people participated in the Eleusinian Mysteries:

Priests, priestesses, and hierophants.
Initiates, undergoing the ceremony for the first time.
Others who had already participated at least once. They were eligible for the fourth category.

Those who had attained épopteia, (English: "contemplation"), who had learned the secrets of the greatest mysteries of Demeter.

Among the participants were probably also influential personalities such as Sokrates, Plato, Aristotle, Sophocles, Plutarch, Hadrian, Julian, and Cicero.

There were two Eleusinian Mysteries, the Greater and the Lesser. The dramatic shows of the Lesser Mysteries occultly signified the miseries of the soul while in subjection to the body, so those of the Greater intimated, by mystic visions, the felicity of the soul both here and hereafter, when purified from the defilements of a material nature and constantly elevated to the realities of intellectual [spiritual] vision. According to Plato, "the ultimate design of the Mysteries … was to lead us back to the principles from which we descended, … a perfect enjoyment of intellectual [spiritual] good.” At some point in the Greater Mysteries there was believed to be the drinking of something called “kykeon,” a barley drink laced with a psychedelic substance to assist visions and enlightenment.

As Christianity gained in popularity in the 4th and 5th centuries, Eleusis's prestige began to fade and the Roman emperor Theodosius I closed the sanctuaries by decree during the Persecution of pagans in the late Roman Empire in 392 AD. Then the last remnants of the Mysteries were wiped out in 396 AD, when Arian Christians under Alaric, King of the Goths, destroyed and desecrated the old sacred sites.