[W]e may say that a Mystery-Religion was (I) a religion of symbolism which, through myth and allegory, iconic representations, blazing lights and dense darkness, liturgies and sacramental acts, and suggestion quickened the intuitions of the heart, and provoked in the initiate a mystical experience conducing to palingenesia (regeneration), the object of every initiation.
-Samuel Angus, The Mystery Religions

The Mystery Cults can best be described as secretive orders centered around individual pagan gods and goddesses. These cults focused on ritual acts, including allegorical purification and spiritual introspection. The main purpose of the Mystery Cults was to purify souls, such that they could escape the physical world and return to the One (the highest good or god). This has to be said in a general sense as the Mystery Religions were not a uniformed belief system, but rather sporadic and divergent cults with varying origins.

These orders derive their names, the Mysteries, from the fact that they professed secret doctrines revealed only to the elect higher ranked initiates. The secrets were kept on pain of death. This is another reason all statements about the Mystery cults must be said with some caution. Recreating the Mystery Cults involves patch-working divergent sources from across centuries of time. Not many sources were willing to temp the punishment for profaning the Mysteries.

Livy records that two youths were executed for mistakenly wandering into the mystery rites:

During the celebration of the mysteries, two young men of Acarnania, who were not initiated, unapprized of its being an offence against religion, entered the temple of Ceres along with the rest of the crowd: their discourse readily betrayed them, by their asking some absurd questions; whereupon, being carried before the presidents of the temple, although it was evident that they went in through mistake, yet they were put to death, as if for a heinous crime.

Other accounts include death threats against the famed Greek Alcibiades and attempted executions of Andokides and Diagoras the Melian. Although the existing historical accounts of penalties seem limited to these instances, we have to be informed by these accounts. The lack of published secrets attest to the effectiveness of suppression of these facts.

Any hint of exposing Mystery secrets always were accompanied by mass outrage and death threats.

Origin

The origins of the Mystery Cults extend as far back to possibly the fifteenth century BC. The Parian Chronicle places Demeter in Eleusis at this time:

12) From when Demeter, coming to Athens, [invented] the seed corn, and the [first festival of ploughing time was celebrated, under the instruction of T]riptolemus, son of Celeus and Neaira, 1146 years, when Erechtheus was king in Athens.

13) From when Tripto[lemus reaped the corn which] he sowed in the Rarian plain called Eleusis, 1[1]45 years, when [Erechtheus] was king of Athens.

Sowing the corn is said by Mystery Religion scholar George Mylonas to be symbolic for participating in the rites in his book Eleusis and the Eleusinian Mysteries.

A Homeric hymn, written in the style of Homer (C. 850BC) probably around the seventh century, also makes mention of these same Mystery Rites:

… Then she went to the kings, administrators of themistes,
and she showed them—to Triptolemos, to Diokles, driver of horses,
to powerful Eumolpos and to Keleos, leader of the people [lâoi]—
she revealed to them the way to perform the sacred rites, and she pointed out the ritual to all of them[51]
—the holy ritual, which it is not at all possible to ignore, to find out about,
or to speak out. The great awe of the gods holds back any speaking out.
Olbios [e.g. prosperous or happy] among earth-bound mortals is he who has seen these things.
But whoever is uninitiated in the rites, whoever takes no part in them, will never get a share [aisa] of those sorts of things [that the initiated get],
once they die, down below in the dank realms of mist.

Although the Mystery Cults started in a polytheistic context, with polytheistic themes, the Greek religion gradually progressed. Philosophers, such as Xenophanes, wrote scathing reviews of the Greek gods, claiming them false and positing a monotheism featuring a god without form. Soon, Greek culture embraced this philosophy. Per Marvin W Meyer in The Ancient Mysteries: A Sourcebook of Sacred Texts:

But for the Greeks of the fifth and forth centuries B.C.E., the heroic days celebrated by the bard Homer in his Iliad and Odyssey represented the old order of the Greek world, and that old order, with its increasingly anachronistic poleis and its out-moded gods, was giving way to a new post-Olympian world…

In sum, the Olympians began to fall from glory for several reasons. Their destiny was linked to that of the Greek polis, which was no longer the basic political unit in the world after Alexander’s time. Furthermore, the philosophical criticism of religion that took place before and during the Hellenistic period challenged Greek beliefs and exposed the gods as unworthy of the worship and devotion of thoughtful Greek people. To be sure, the Olympian pantheon maintained itself as a religious and cultural force in the Hellenistic world, and attempts were made to inject new philosophical and religious values into the systems of the Olympian deities. Homer did not relinquish his place at the center of ancient education, and the allegorical exegesis of Homeric texts allowed people to interpret the sacred myths in new, scientific, philosophical ways. Nonetheless, the hearts of many were turning away from Zeus and the Olympians during this period, and many searched at home and abroad for gods that would satisfy more fully their religious longings.

By the time of Plato, the popular Mystery Cults embraced much of what is commonly called Platonism, while rejecting the myths of Homer.

Rites

The Mystery Cults are most associated with their rites. These rites were major celebrations in the ancient world and would attract large crowds of distant peoples (people who were initiated and those who wished to be initiated). The rites usually took for form of symbolic gestures mimicking specific cultic myths. The rites, especially the rites of Eleusis, often symbolize death and rebirth.

The Eleusinian rites were the most popular. They used the fable of Demeter and Persephone (Kore) as their basic mythology. Dudley Wright describes the story:

Persephone (sometimes described as Proserpine and as Cora or Kore), when gathering flowers, was abducted by Pluto, the god of Hades, and carried off by him to his gloomy abode… Demeter (or Ceres), her mother, arrived too late to assist her child… For nine nights and days she wandered, torch in hand, in quest of her child… Demeter was still vowing vengeance against gods and men, and because of the continued loss of her daughter she rendered the earth sterile during a whole year.

…

The oxen drew the plough, but in vain was the seed sown in the prepared ground. Mankind was threatened with utter annihilation, and all the gods were deprived of sacrifices and offerings. Zeus endeavoured to appease the anger of the gods, but in vain. Finally he summoned Hermes to go to Pluto and order him to restore Persephone to her mother. Pluto yielded, but before Persephone left she took from the hand of Pluto four pomegranate pips which he offered her as sustenance on her journey. Persephone, returning from the land of shadows, found her mother in the temple at Eleusis which had recently been erected. Her first question was whether her daughter had eaten anything in the land of her imprisonment, because her unconditional return to earth and Olympos depended upon that. Persephone informed her mother that all she had eaten was the pomegranate pips, in consequence of which Pluto demanded that Persephone should sojourn with him for four months during each year, or one month for each pip taken. Demeter had no option but to consent to this arrangement, which meant that she would enjoy the company of Persephone for eight months in every year, and that the remaining four would be spent by Persephone with Pluto. Demeter caused to awaken anew “the fruits of the fertile plains,” and the whole earth was re-clothed with leaves and flowers…

The entire myth is centered around the concept of a death and rebirth. Persephone descends to hades, but returns. Plants wither and die, yet spring again to life. This continues indefinitely. This story served as ample bedrock for the Mystery rites. The Eleusinian Mysteries were split into two parts, the Greater and the Lesser Mysteries. The Greater Mysteries honored Demeter and the descent. The Lesser Mysteries honored Persephone and the reawakening.

The Greater rites have described most fully by George Mylonas in his book Eleusis and the Eleusinian Mysteries:

Day 0 – priestesses carried a basket of Sacred Objects from Eleusis to Athens.
Day 1 – Initiates gathered, vowed silence, and began fasting.
Day 2 – Initiates formed a procession to the sea to begin purification.
Day 3 – Each initiate sacrificed a pig for that evening’ feast.
Day 4 – Each initiate would undergo healing rites and try to harvest their dreams for interpretation.
Day 5 – A grand procession is formed to march back to Eleusis, stopping at the various places that Demeter was said to have stopped.
Day 6 – A nightlong party and subsequent day of rest.
Day 7 – Mystery initiates would enter the temple are night to fulfill the rest of the Demeter myth, including death and rebirth. This stage was much more secretive. It is here that initiates viewed of some sort of sacred object, or focus item. Hippolytus (although not a disinterested witness) relates that the focus item was an ear of corn. This ear of corn represented “perfect enormous illumination”:

And after the Phrygians, the Athenians, while initiating people into the Eleusinian rites, likewise display to those who are being admitted to the highest grade at these mysteries, the mighty, and marvellous, and most perfect secret suitable for one initiated into the highest mystic truths: (I allude to) an ear of corn in silence reaped. But this ear of corn is also (considered) among the Athenians to constitute the perfect enormous illumination (that has descended) from the unportrayable one…

Focus items were not special in and of themselves, but an object on which initiates could contemplate greater truths. These focus items seem to be a common object in all Mystery Cults. In fact, when Pompey invades Jerusalem he is surprised that he finds nothing when invading the Jewish temple. He was expecting some sort of focus item or statue, anything. But it is empty, and Pompey discounts the Jewish “mysteries” as empty:

[5.9] Gnaeus Pompeius was the first of our countrymen to subdue the Jews. Availing himself of the right of conquest, he entered the temple. Thus it became commonly known that the place stood empty with no similitude of gods within, and that the shrine [mysteries] had nothing to reveal [were a sham].

After this focus item is viewed and contemplated. There seems to be some sort of rebirth ritual. Themistios records:

The soul [at death] has the same experience as those who are being initiated into great Mysteries… at first one wanders and wearily hurries to and fro, and journeys with suspicion through the dark as one uninitiated: then come all the terrors before the final initiation, shuddering, trembling, sweating, amazement: then one is struck with a marvelous light, one is received into pure regions and meadows, with voices and dances and the majesty of holy sounds and shapes: among these he who has fulfilled initiation wanders free, and released and bearing his crown joins in the divine communion, and consorts with pure and holy men.

The culmination of the entire rite is some sort of other-bodily experience. Initiates experience death but then become enlightened and reborn.

Another account of the Mystery rites is in the satirical book The Golden Ass, by Apuleius. This book is also known as Metamorphoses, a novel in which the narrator magically turns himself into a donkey. But in Book 11, the narrator becomes an initiate into the Mysteries of Isis:

At once I set about acquiring those things myself or procuring them zealously through friends, while sparing no expense. Then the high-priest escorted by a band of devotees led me to the nearest baths, saying the occasion required it. When I had bathed according to the custom, he asked favour of the gods, and purified me by a ritual cleansing, sprinkling me with water. Then in the early afternoon he led me to the shrine again, and placed me at the Goddess’ feet. He gave me certain orders too sacred for open utterance then, with all the company as witnesses, commanded me to curb my desire for food for the ten days following, to eat of no creature, and drink no wine.

We see the familiar theme of cleansing and fasting in preparation of what is to come. Apuleius also speaks about several dreams and his conversations with the priests about them. Apuleius later becomes an initiate of Osiris, and the same thing is repeated, but this time without the baptism (does the Isis baptism count for both?):

I made my preparations, again went without meat for a ten day period, and shaved my head, after which I was initiated into the nocturnal mysteries of the supreme god, and confidently enacted the holy rites of his worship too…

All of these rites, Apuleius relates, are about death and rebirth:

The gates of the underworld and the guardianship of life are both in her hands, he said, and the rites of initiation are akin to a willing death and salvation through her grace. Indeed, those whose term of life was drawing to its close, who already stood on the last threshold of light, if the sect’s unspoken mysteries could be safely entrusted to them, were often summoned by the power of the Goddess to be in a manner reborn through her grace and set again on a path of renewed life.

This rebirth, as related by Plato and Plotinus, was an equivalent of a Platonic ascent, a return to the One.

Theology

Olbios [blessed] among earth-bound mortals is he who has seen these things.
But whoever is uninitiated in the rites, whoever takes no part in them, will never get a share [aisa] of those sorts of things [that the initiated get], once they die, down below in the dank realms of mist.
-Hymn to Demeter

Beautiful indeed is the Mystery given us by the blessed gods: death is for mortals no longer an evil, but a blessing.
-Inscription found at Eleusis

Both Plato (428 – 347BC) and Plotinus (204-270AD) speak about the end goals of the Mystery Cults.

From Plato in Phaedo:

And I conceive that the founders of the mysteries had a real meaning and were not mere triflers when they intimated in a figure long ago that he who passes unsanctified and uninitiated into the world below will live in a slough, but that he who arrives there after initiation and purification will dwell with the gods. For “many,” as they say in the mysteries, “are the thyrsus bearers, but few are the mystics,”-meaning, as I interpret the words, the true philosophers.

But he who is a philosopher or lover of learning, and is entirely pure at departing, is alone permitted to reach the gods. And this is the reason… why the true votaries of philosophy abstain from all fleshly lusts, and endure and refuse to give themselves up to them-not because they fear poverty or the ruin of their families, like the lovers of money, and the world in general; nor like the lovers of power and honor, because they dread the dishonor or disgrace of evil deeds.

In Phaedrus, Plato relates:

Ten thousand years must elapse before the soul of each one can return to the place from whence she came, for she cannot grow her wings in less; only the soul of a philosopher, guileless and true, or the soul of a lover, who is not devoid of philosophy, may acquire wings … But the others receive judgment when they have completed their first life, and after the judgment they go, some of them to the houses of correction which are under the earth, and are punished; others to some place in heaven whither they are lightly borne by justice… For a man must have intelligence of universals, and be able to proceed from the many particulars of sense to one conception of reason;-this is the recollection of those things which our soul once saw while following God-when regardless of that which we now call being she raised her head up towards the true being. And therefore the mind of the philosopher alone has wings; and this is just, for he is always, according to the measure of his abilities, clinging in recollection to those things in which God abides, and in beholding which He is what He is. And he who employs aright these memories is ever being initiated into perfect mysteries and alone becomes truly perfect. But, as he forgets earthly interests and is rapt in the divine, the vulgar deem him mad, and rebuke him; they do not see that he is inspired.

The Mystery Cults embraced rebirth. This took the form of depreciation from partaking in the physical world. The physical world was something to be escaped. Those who succeed at initiation will “dwell with the gods”. This idea that Mystery initiates would be reborn into the spiritual world is also related by Plotinus around 600 years later. From Plotinus:

7. Therefore we must ascend again towards the Good, the desired of every Soul. Anyone that has seen This, knows what I intend when I say that it is beautiful. Even the desire of it is to be desired as a Good. To attain it is for those that will take the upward path, who will set all their forces towards it, who will divest themselves of all that we have put on in our descent:- so, to those that approach the Holy Celebrations of the Mysteries, there are appointed purifications and the laying aside of the garments worn before, and the entry in nakedness- until, passing, on the upward way, all that is other than the God, each in the solitude of himself shall behold that solitary-dwelling Existence, the Apart, the Unmingled, the Pure, that from Which all things depend, for Which all look and live and act and know, the Source of Life and of Intellection and of Being.

The writings of Plato show some development of this Platonistic Dualism in the Mystery Cults. This idea matured by the time of Plotinus. The Mystery Cults generally adopted the idea that the physical world was evil and the goal of a religious life was to disdain the flesh and ascend to the divine. The divine was pure and indescribable. It was the Platonistic idea of the One (the ultimate good). It would be hard to imagine that Plato did not influence the Mystery Cults, not unlike how the Mystery Cults influenced Plato. Certainly it makes sense that the enlightened secrets of the mystery cults were some sort of path in order to ascend to the One.

Plato writes:

There was a time when with the rest of the happy band they saw beauty shining in brightness, – we philosophers following in the train of Zeus, others in company with other gods; and then we beheld the beatific vision and were initiated into a mystery which may be truly called most bleed, celebrated by us in our state of innocence before we had any experience of evils to come, when we were admitted to the sight of apparitions innocent and simple and calm and happy, which we beheld shining in pure light.

Conclusion

The Mystery Cults served as symbolically based conduits to the Platonistic ascent. In the 18th century book, The Divine Legation of Moses, the author argues that the primary secret of the Mystery cults was that God is Unity, the One. This “secret” is obvious to anyone who is familiar with Greek writings. Most Greeks, by the time of Plato, were monotheistic in the sense they believed in this One. The secrets of the Mystery Cults were actually that man can ascend to the Unity, the One. This was the point of all their secretive rites, a hope in eternal life unified with godhood.