Exorcism is a religious procedure during which demons, evil spirits or other spiritual entities are ‘driven’ or ‘cast’ out of a person or place believed to be possessed (under the control of these entities).
The Holman Bible Dictionary explains exorcism from a Christian perspective as:
The practice of expelling demons by means of some ritual act. Although the Hebrew Bible does make reference to demonic beings (Lev. 17:7; Deut. 32:17; Isa. 13:21; 34:14; 2 Chron. 11:15; Ps. 106:37 NRSV), there is no account of demons being cast out of a person or a place. The office of the exorcist, long known in the religious practice of Mesopotamia, is totally absent from the Hebrew Bible. The demons that are mentioned there are usually dreadful earthly beings, sometimes resembling goats or satyrs who live in dry regions. Twice a loan-word, shedim (Akkadian: shedu, “protecting spirit”), is used to describe the foreign gods (Deut. 32:17; Ps. 106:37) and is usually translated “demons” in English.
In the New Testament the demons were earthly powers or spirits allied with Satan. Jesus’ power to exorcise is demonstration in the Synoptic Gospels of His power over Satan (Matthew 15:21-28; Mark 1:23-38; 5:1-20; 7:24-30; 9:14-29). Exorcism is included in the list of wonders Jesus performed at Capernaum and in the Galilee (Mark 1:34,39). Mark 3:11 reports that Jesus had to silence the unclean spirits because they recognized Him and proclaimed Him Son of God.
Jesus gave His disciples authority over unclean spirits (Mark 3:14-15; 6:7) which they generally exercised with success (Mark 6:13), but not always (Mark 9:18). Mark 9:38-41 makes reference to someone who did exorcisms in the name of Jesus even though he was not a follower of Jesus. Jesus told the disciples not to forbid him. In another vein, Acts 19:13-16 tells of wandering Jewish exorcists in Ephesus who attempted to exorcise demons in the name of the Jesus preached by Paul but without success.
John says nothing of Jesus exorcising demons, but the issue of demons is not lacking in that Gospel, for His opponents often accused Jesus of being possessed (John 7:20; 8:48-49,52; 10:20). Similarly, in the Synoptics, the scribes accused Him of casting out demons by the power of the prince of demons (Mark 3:22).
The usual technique of exorcism, as shown by contemporary magical papyri, was to adjure the demon (by name, if possible) through the power of one or more gods to depart the one possessed. This was often accompanied by preparations of herbs and the imposition of amulets. Magical words of extended, repeated syllables were also part of almost all exorcistic formulas. By contrast, the exorcisms of Jesus in the Synoptics involved His command without reference to other divine beings (Mark 1:25; 9:25) and with only a single reference to anything like technique in saying about the boy the disciples could not exorcise that the demon involved could only be cast out by prayer (Mark 9:29). Something close to the usual technique of exorcism was demonstrated by the Gerasene demoniac who tried unsuccessfully to exorcise Jesus, calling Him by title and adjuring Him in the name of the Most High God to leave him alone (Mark 5:7). Jesus relied on His own unique power to demonstrate demons had no place or power in His Kingdom.
– Source: Fred L. Horton, Jr., Holman Bible Dictionary 1
Exorcism Often Goes Wrong
Religion News Blog’s archive of news articles related to exorcism shows that many so-called ‘exorcisms’ — particular when applied by lay people — go wrong. Many such exorcism result in the death of the person being ‘treated,’ and lead to murder charges for those involved.
We list research resources on this topic in our entry on Demonology, Demon Possession