"Theurgy" describes the practice of rituals, sometimes seen as magical in nature, performed with the intention of invoking the action of God (or other personified supernatural power), especially with the goal of uniting with the divine, or perfecting or improving oneself.

Neoplatonism

The source of Western theurgy can be found in the philosophy of late Neoplatonists, especially Iamblichus. In late Neoplatonism, the universe is regarded as a series of emanations from the Godhead. Matter itself is merely the lowest of these emanations, and therefore not in essence different from the Divine. Although the number and qualities of these emanations differ, most Neoplatonists insisted that God was both singular and good. Although Neoplatonists were technically polytheists, they also embraced a form of monism: reality was varied, with varied gods, but they all represented aspects of the one reality.

For Plotinus, Iamblichus' teacher, the emanations are as follows:

• To En (τό ἕν), "the One": Deity without quality, sometimes called "The Good."
• Nous (Νοῦς), "Mind": The Universal consciousness, from which proceeds
• Psychè (Ψυχή), "Soul": Including both individual and "world souls," leading finally to
• Physis (Φύσις), "Nature".

Plotinus urged contemplations for those who wished to perform theurgy, the goal of which was to reunite with God. Therefore, his school resembles a school of meditation or contemplation. His student, Iamblichus of Syria, taught a more ritualized method of theurgy, that apparently involved invocation and religious, as well as magic, ritual. Iamblichus believed theurgy was an imitation of the gods, and in his major work, On the Egyptian Mysteries, he described theurgic observance as "ritualized cosmogony" that endowed embodied souls with the divine responsibility of creating and preserving the cosmos.

Emperor Julian

The Emperor Julian (332-363), sometimes called Julian the Apostate, embraced Neoplatonic philosophy and worked to replace Christianity with his own version of Neoplatonic paganism. Due to his short reign, this was ultimately unsuccessful, but he did produce several works of philosophy and theology, including a hymn to the sun. In his theology, Helios, the Sun, was the perfect example of God's perfection and light, a symbol of divine emanation. He also held the mother goddess Cybele in high esteem.

Julian favored ritual theurgy, with an emphasis on sacrifice and prayer. He was heavily influenced by the ideas of Iamblichus.

Kabbalah

A system of Jewish mysticism known as the Kabbalah displays many Neoplatonic elements, and some writers, such as Kieron Barry , have argued that the Kabbalah has an ultimately Greek origin. In the Kabbalah, God creates the universe through ten sephiroth, or vessels. These are, in order:

1. Kether, Crown
2. Khokmah, Wisdom
3. Binah, Understanding
4. Khesed, Mercy
5. Givurah, Strength
6. Tifareth, Beauty
7. Netzakh, Victory
8. Hod, Glory
9. Yesod, Foundation
10. Malkuth, Kingdom

These ten sephiroth are linked by twenty-two paths, corresponding to the letters of the Hebrew alphabet.

Many of the similarities are cosmetic: for example, in the Kabbalah there is a strong sense that the emanations are trinary in nature, each pair producing the next in a process of synthesis. In Greek Neoplatonism, this is not the case: usually, emanations are linear, each leading to the next. Also, in the Kabbalah, the letters of the Hebrew alphabet are, themselves, regarded as having some divine power. Although there is some evidence for similar attitudes in Greek theurgy, there they are not as developed.

Christian theurgy

One may regard the Christian mass as a form of theurgy, in which the power of Christ is called down into the host and hence into its consumer. The practice of the Novena could also be interpreted as theurgy, although it borders more on practical folk magic. Similarly, contemplative Christian practices, such as constant recitation of the Jesus Prayer, are theurgic in goal and — at least from the perspective of Plotinus — method.

Christian magical practices, such as those practiced by the Hermetic Order of the Golden Dawn, borrow heavily from Neoplatonic and Cabalistic sources. The ultimate goal of such practices is not practical, worldly power, but uniting with God through ritual and contemplation.