The historians who study the issue tend to agree that Plato was initiated into the Mystery Cults of his time. Some say that he was singled out for revealing secret information about their teachings, although I have not found anything substantive on the issue.
In Phaedo, Plato gives a reader a sense of the ultimate purpose of the Mystery Cults. Remember, the Mystery Cults had a sweeping influence on the early Christian Church. Much of the Mystery Cult religions were intertwined with Platonism. Plato writes:
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.
The purpose of the Mystery Cults was to achieve enlightenment, in order to pass onto a higher state of being after death. Plato continues:
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, Simmias and Cebes, 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.
Plato, speaking of the mystery cults and philosophers, points to disdain for physical pleasures (asceticism). Purging the physical pleasures helped the mystery cultists achieve purity. It was then they could “reach the gods.”
The lovers of knowledge are conscious that their souls, when philosophy receives them, are simply fastened and glued to their bodies: the soul is only able to view existence through the bars of a prison, and not in her own nature; she is wallowing in the mire of all ignorance; and philosophy, seeing the terrible nature of her confinement, and that the captive through desire is led to conspire in her own captivity (for the lovers of knowledge are aware that this was the original state of the soul… philosophy shows her that this is visible and tangible, but that what she sees in her own nature is intellectual and invisible. And the soul of the true philosopher thinks that she ought not to resist this deliverance, and therefore abstains from pleasures and desires and pains and fears, as far as she is able; reflecting that when a man has great joys or sorrows or fears or desires he suffers from them, not the sort of evil which might be anticipated-as, for example, the loss of his health or property, which he has sacrificed to his lusts-but he has suffered an evil greater far, which is the greatest and worst of all evils, and one of which he never thinks.
The end state, of the Mystery Religions was one in which the philosopher understood that the soul and body are separate beings, that the soul would return to an intellectual and invisible state, and that the physical, material world should be shunned. The Mystery Religions were an early form of Neoplatonism.