Exorcism
In Catholic practice the person performing the exorcism, known as an exorcist, is an ordained priest. The exorcist recites prayers according to the rubrics of the rite, and may make use of religious materials such as icons and sacramentals. The exorcist invokes God—specifically the Name of Jesus—as well as members of the Church Triumphant and the Archangel Michael to intervene with the exorcism. According to Catholic understanding, several weekly exorcisms over many years are sometimes required to expel a deeply entrenched demon.
Exorcism in Christianity
The traditional method for determining if a person needs a deliverance is done by having someone present who has the gift of discerning of spirits. This is a gift of the Holy Spirit from 1 Corinthians 12 that allows a person to "sense" in some way an evil presence. While the initial diagnosis is usually uncontested by the congregation, when many people are endowed with this gift in a single congregation, results may vary.