Mystery-term popularized by Iamblichus for a method of individual communion with the gods, or bringing the gods down to earth. It consisted in purifying the psycho-astral links between the mind and its divine counterpart, whereby the theurgist was not only brought into conscious communion with his own higher self, but also with other divine entities. The first school in the Christian period "was founded by Iamblichus among certain Alexandrian Platonists. The priests, however, who were attached to the temples of Egypt, Assyria, Babylonia and Greece, and whose business it was to evoke the gods during the celebration of the Mysteries, were known by this name, or its equivalent in other tongues, from the earliest archaic period. Spirits (but not those of the dead, the evocation of which was called Necromancy) were made visible to the eyes of mortals. Thus a theurgist had to be a hierophant and an expert in the esoteric learning of the Sanctuaries of all great countries. The Neo-platonists of the school of Iamblichus were called theurgists, for they performed the so-called 'ceremonial magic,' and evoked the simulacra or the images of the ancient heroes, 'gods,' and daimonia ( {Greek char} divine, spiritual entities). In the rare cases when the presence of a tangible and visible 'spirit' was required, the theurgist had to furnish the weird apparition with a portion of his own flesh and blood -- he had to perform the theopaea, or the 'creation of gods,' by a mysterious process well known to the old, and perhaps some of the modern, Tantrikas and initiated Brahmans of India" (TG 329-30).

The varied uses by different writers shows the term's applicability to a considerable range of practices.

"The popular prevailing idea is that the theurgists, as well as the magicians, worked wonders, such as evoking the souls or shadows of the heroes and gods, and other thaumaturgic works, by supernatural powers. But this never was the fact. They did it simply by the liberation of their own astral body, which, taking the form of a god or hero, served as a medium or vehicle through which the special current preserving the ideas and knowledge of that hero or god could be reached and manifested" (TG 330).

Plotinus was opposed to theurgy, and Porphyry says that it can but cleanse the lower or psychic portion and make it capable of perceiving lower beings, such as spirits, angels, and gods; it is powerless to purify the noetic or manasic (intellectual) principle. But Porphyry was persuaded by his master Iamblichus to concede the value of theurgy under certain limitations. Porphyry's views highlight the difference between raja yoga and hatha yoga. In the case of such a person as Iamblichus, practices might be quite safe which would be fraught with nothing but harm in the hands of another or without the help of such a teacher. For once the barriers are down a way is opened for communion with all kinds of undesirable entities, against which the experimenter will not know how to protect himself.

In the ancient Mysteries, theurgy was divided into different degrees. To illustrate, in one of the highest initiatory degrees the initiant was brought face to face with the divinity within himself, and in order to accomplish this the initiant had to give of his own spiritual and intellectual substance and vitality so that his inner god might imbody itself on inner and invisible planes, the rite thus providing a temporary and illusory divorce which was really an essential union of the divine in man with the spiritual-intellectual -- the latter recognizing for the time being its own divine origin and coalescing with it. In a less perfect form of such theurgical practice, and in a lower degree of the Mysteries, the initiant gave of his own astral and physical substance, the effluvia of his astral body and of his flesh and blood, to provide a vehicle through which a spiritual entity might have a tangible, although very temporary, imbodiment; and for the time being the initiant was thus enabled to see, touch, and converse with a being of the inner worlds who otherwise would have been utterly unable to enter our physical sphere except by those spiritual-akasic currents of forces which human beings recognize as inspiration.