Further, in that ancient world the one live form of religion was to be found in the Mystery Religions. The one thing the Mystery Religions offered was communion and even identity with some god. The way it was done was this. All the Mystery Religions were essentially passion plays. They were stories of a god who had lived and suffered terribly and who died and rose again. The story was turned into a moving play. Before the initiate could see it, he had to undergo a long course of instruction in the inner meaning of the story. He had to undergo all kinds of ceremonial purifications. He had to pass through a long period of fasting and abstention from sexual relationships.
At the actual presentation of a passion play everything was designed to produce a highly emotional atmosphere. There was carefully calculated lighting, sensuous incense, exciting music, a wonderful liturgy; everything was designed to work up the initiate to a height of emotion and expectation that he had never experienced before. Call it hallucination if you like; call it a combination of hypnotism and self hypnotism. But something happened; and that something was identity with the god. As the carefully prepared initiate watched he became one with the god. He shared the sorrows and the griefs; he shared the death, and the resurrection. He and the god became for ever one; and he was safe in life and in death.
Some of the sayings and prayers of the Mystery Religions are very beautiful. In the Mysteries of Mithra the initiate prayed: "Abide with my soul; leave me not, that I may be initiated and that the holy spirit may dwell within me." In the Hermetic Mysteries the initiate said: "I know thee Hermes, and thou knowest me; I am thou and thou art I" In the same Mysteries a prayer runs: "Come to me, Lord Hermes, as babes to mothers' wombs." In the Mysteries of Isis the worshipper said: "As truly as Osiris lives, so shall his followers live. As truly as Osiris is not dead, his followers shall die no more."
We must remember that those ancient people knew all about the striving, the longing, the dreaming for identity with their god and for the bliss of taking him into themselves. They would not read phrases like eating Christ's body and drinking his blood with crude and shocked literalism. They would know something of that ineffable experience of union, closer than any earthly union, of which these words speak. This is language that the ancient world could understand--and so can we.
William Barclay, The Gospel of John (Volume 1), p. 221-223