Below is an excerpt from Mircea Eliade's 1958 book, "Rites And Symbols of Initiation: The Mysteries of Birth and Rebirth." Harper & Row, Publishers: New York. Pg. 112-15.
For the purpose of our investigation, one thing is particularly of interest---that these experiences are brought on by rites which, both in the Greco-Oriental and the primitive worlds, are initiatory, that is, pursue the novice's spiritual transmutation. At Eleusis, as in the Orphic-Dionysiac ceremonies, as in the Greco-Oriental mysteries of the Hellenistic period, the mystes submits himself to initiation in order to transcend the human condition and to obtain a higher, superhuman mode of being. The initiatory rites reactualize an origin myth, which relates the adventures, death, and resurrection of a Divinity. We know very little about these secret rites, yet we know that the most important of them concerned the death and mystical resurrection of the initiand.On Christianity borrowing from the mysteries: (Pg. 121)
On the occasion of his initiation into the mysteries of Isis, Apuleius suffered a "voluntary death" (ad instar voluntariae mortis) and "approached the realm of death" to obtain his "spiritual birthday" (natalem sacrum). The exemplary model for these rites was the myth of Osiris. It is probable that in the mystery of the Phrygian Great Mother---and perhaps elsewhere too---the mystes was symbolically buried in a tomb. According to Firmicus Maternus, he was regarded as moriturus, "about to die." This mystical death was followed by a new, spiritual birth. In the Phrygian rite, Sallustius records, the new initiates "received nourishment of milk as if they were being reborn." And in the text which is known under the title of the Liturgy of Mithra, but which is pervaded with Hermetic Gnosticism, we read: "Today, having been born again by thee, out of so many myriads rendered immortal . . ." or "Born again for rebirth of that life-giving birth . ."
Everywhere there is this spiritual regeneration, a palingenesis, which found its expression in the radical change in the mystes' existential status. By virtue of his initiation, the neophyte attained to another mode of being; he became equal to the Gods, was one with the Gods. Apotheosis, deification, demortalizing (apathanatismos) are concepts familiar to all the Hellenistic mysteries. Indeed, for antiquity in general, the divinization of man was not an extravagant dream. "Know, then, that you are a God," Cicero wrote. And in a Hermetic text we read: "I know thee, Hermes, and thou knowest me: I am thou and thou art I." Similar expressions are found in Christian writings. As Clement of Alexandria says, the true (Christian) Gnostic "has already become God." And for Lactantius, the chaste man will end by becoming consimilis Deo, "identical in all respects with God."
The ontological transmutation of the initiate was proved above all through his existence after death. The Homeric Hymn to Demeter, Pindar, and Sophocles already praise the bliss of initiates in the Other World, and pity those who die without having been initiated. In the Hellenistic period the idea that he who had been initiated into the mysteries enjoyed a privileged spiritual situation, both during life and after death, had become increasingly widespread. Those who submitted to initiation, then, sought thereby to obtain a superhuman ontological status, more or less divine, and to ensure their survival after death, if not their immortality. And, as we have just seen, the mysteries employ the classic pattern: mystical death of the initiand, followed by a new, spiritual birth.
For the history of religion, the particular importance of the Greco-Oriental mysteries lies in the fact that they illustrate the need for a personal religious experience engaging man's entire existence, that is, to use Christian terminology, as including his "salvation" in eternity. Such a personal religious experience could not flourish in the framework of the public cults, whose principal function was to ensure the sanctification of communal life and the continuance of the State. In the great historical civilizations in which the mysteries proliferated, we no longer find the situation characteristic of primitive cultures; there, as we have noted more than once, the initiations of the youth were at the same time an occasion for the completely regeneration not only of the collectivity but also of the cosmos. In the Hellenistic period we find an entirely different situation; the immense success of the mysteries illustrates the break between the religious elites and the religion of the State, a break that Christianity will widen and, at least for a time, make complete.
But for our present investigation the interest of the mysteries lies in the fact that they demonstrate the perennial significance of the traditional patterns of initiation and their capacity for being indefinitely reanimated and enriched with new values. In the Hellenistic world we find the same state of things that we observed in India; an archaic pattern can be taken over and utilized for many various spiritual ends, from mystical union with the Deity to the magical conquest of immortality or the achievement of final deliverance, nirvana. It is as if initiation and its patterns were indissolubly linked with the very structure of spiritual life; as if initiation were an indispensable process in every attempt at total regeneration, in every effort to transcend man's natural condition and attain to a sanctified mode of being. Equally significant is the fact that the imagery of the mysteries finally permeated an immense philosophical and spiritualistic literature, particularly in late antiquity. Homologizing philosophy to initiation had been a common motif even from the beginnings of Pythagoreanism and Platonism. But the maieutic procedure (from the root maia, "midwife") by which Socrates sought to "deliver" a new man had its prototype in archaic societies, in the work of the masters of initiation; they too delivered neophytes, that is, helped them to be born to spiritual life. Toward the end of antiquity the motif of initiatory delivery was accompanied by the theme of spiritual paternity, a theme already documented for Brahmanism and late Buddhism. (See pp. 53 ff.) St Paul has "spiritual sons," sons whom he has engendered by faith.
But this is only a beginning. Though abstaining from revealing the secrets of the various Hellenistic mysteries, many philosophers and theosophists propounded allegorical interpretations of the initiatory rites. The majority of these interpretations referred the rites of the mysteries to the successive stages through which the human soul must pass in its ascent to God. Any acquaintance with the works of Iamblichus, Proclus, Synesius, Olympiodorus, as of many other Neoplatonists or theosophists of the last centuries of antiquity, suffices to show how completely they assimilated the mystery initiations to a psychodrama through which the soul can free itself from matter, attain regeneration, and take its flight to its true home, the intelligible world. In making this assimilation these writers were continuing a process of spiritual revaluation that had already found expression the mysteries of Eleusis. There too, at a certain moment in history, an agricultural ritual had been charged with new religious values. Though preserving its primitive agricultural structure, the mystery no longer referred to the fertility of the soil and the prosperity of the community, but to the spiritual destiny of each individual mystes. The late commentators were innovators only in the sense that they read their own spiritual situations, determined by the profound crisis of their times, into the ancient rites.
Hence it is doubtful if this enormous mass of hermeneutic writing is of any service in an attempt to discover the original meaning of the Eleusinian, Orphic, or Hellenistic mysteries. But if these allegorical interpretations cannot put us in possession of historical realities, they are nevertheless of considerable value. For such interpretations characterize the entire history of later syncretistic spirituality. It was here that that the countless Gnosticisms, both Christian and heterodox, of the first centuries of our era found their ideologies, their symbols, their key images. The touching drama of the human soul blinded and wounded by forgetfulness of its true self was set forth by Gnostic writers with the help of scenarios that finally derived from philosophical exegesis of the mysteries. It was through these syncretistic Gnosticisms that the interpretation of the Hellenistic mysteries as a ritually guided experience of the regeneration of the soul spread through Europe and into Asia. Certain aspects of this mysteriosophy survived even quite late into the Middle Ages. Finally the entire doctrine took on new life, in literary and philosophical circles, through the rediscovery of Neoplatonism in the Italy of the Renaissance.
For our purpose it is important to note that, together with Neoplatonic philosophy, the first values to be accepted by Christianity were the initiatory themes and the imagery of the mysteries. Christianity took the place of the mysteries, as it took the place of the other religious forms of antiquity. The Christian initiation could not coexist with initiations into the mysteries. Otherwise the religion that sought to preserve at least the historicity of Christ would have been in grave danger of becoming indistinguishably confused with the countless syncretistic Gnosticisms and religions. The intolerance of Christianity in its hour of triumph is the most striking proof that no confusion with the Hellenistic mysteries was possible. For the fact is that even Christianity, a revealed religion which did not originally imply any secret rite, which had proclaimed and propagated itself in the broad light of day and for all men, came in the end to borrow from the liturgies and the vocabulary of the Hellenistic mysteries. Morphologically speaking, Christianity too comprises an initiatory pattern---if only by the fact that baptism symbolizes the catechumen's mystical death and resurrection in Christ. It would be needless to insist on the radical differences in religious content that separate the Christian mysterion from the Hellenistic mysteries; for, as the result of a succession of profound and thoroughly documented studies, those differences are today clear. But in estimating the role and the importance of initiation in the religious life of humanity, it is not without interest to record the fact that certain initiatory themes were taken over and revaluated by Christianity.