“A medium of olden times, like the modern “medium” was subject to be entranced at the will and pleasure of the “power” which controlled him; therefore, he could not well have been entrusted with the awful secrets of the final initiation, “never to be revealed under the penalty of death.” The old sage, in unguarded moments of “spiritual inspiration”, revealed that which he had never learned; and was therefore put to death as an atheist.
How then, with such an instance as that of Socrates, in relation to the visions and spiritual wonders at the epoptai, of the Inner Temple, can anyone assert that these seers, theurgists, and thaumaturgists were all “spirit-mediums”? Neither Pythagoras, Plato, nor any of the later more important Neo-Platonists; neither Iamblichus, Longinus, Proclus, nor Apollonius of Tyana, were ever mediums; for in such case, they would not have been admitted to the Mysteries at all.
As Taylor proves – “This assertion of divine visions in the Mysteries is clearly confirmed by Plotinus. And in short, that magical evocation formed a part of the sacerdotal office in them, and that this was universally believed by all antiquity long before the era of the later Platonists”, shows that apart from natural “mediumship”, there has existed, from the beginning of time, a mysterious science, discussed by many, but known only to a few.
The use of it is a longing toward our only true and real home – the after-life, and a desire to cling more closely to our parent spirit; abuse of it is sorcery, witchcraft, black magic. Between the two is placed natural “mediumship”; a soul clothed with imperfect matter, a ready agent for either the one or the other, and utterly dependent on its surroundings of life, constitutional heredity – physical as well as mental – and on the nature of the “spirits” it attracts around itself. A blessing or a curse, as fate will have it, unless the medium is purified of earthly dross.
The reason why in every age so little has been generally known of the mysteries of initiation, is twofold. The first has already been explained by more than one author, and lies in the terrible penalty following the least indiscretion. The second, is the superhuman difficulties and even dangers which the daring candidate of old had to encounter, and either conquer, or die in the attempt, when, what is still worse, he did not lose his reason.
There was no real danger to him whose mind had become thoroughly spiritualized, and so prepared for every terrific sight. He who fully recognized the power of his immortal spirit, and never doubted for one moment its omnipotent protection, had naught to fear. But woe to the candidate in whom the slightest physical fear – sickly child of matter – made him lose sight and faith in his own invulnerability. He who was not wholly confident of his moral fitness to accept the burden of these tremendous secrets, was doomed.”
H. P. Blavatsky
The Mark Of God: Understanding Your "I AM Presence" 