Theurgy was the conjuring of beneficent spirits using an appropriate ritual to employ the superior powers of supernatural beings for earthly purposes. This belief in the power of sympathy was present in classical times but it experienced a great resurgence under the stimulus of Renaissance Neo-Platonism.
Formulas and rituals for spirit-raising were outlined in works such as the Key of Solomon, the Constitution of Honorius, and the Liber Spirituum. The formulas usually involved procedures like drawing chalk circles on the ground, incantations, fasting and prayer. The rituals used holy water, candles, scepters, swords, wands, and metals in what was called the “notary” art because of its inventory of marks and signs. A strong wind was commonly understood to indicate the presence of the supernatural.
Invoking spirits became so common and extensively practiced that it was seen as the stock-in-trade of magical activity and one expected to provide a short-cut to wealth, love, knowledge, and power in all its forms. It also could assist on a more practical level, allowing one to win a lawsuit, escape arrest, and even win at cards.
However, invoking the action, and especially evoking the presence, of one or more gods also had a nobler goal -- that of uniting with the divine to purify and perfect the individual. Summoning celestial beings had an essentially religious dimension which only prayer, piety, and purity of life made possible. In this sense, the spiritual magic of theurgy was a rigorous ascent to God through prayer, fasting, devotion, and humble preparation that no mechanical manipulation of a set formula could achieve.