This is a couple of pages from Reader's Digest Mysteries of The Bible (1988) you might find interesting:
Many people of Jesus’ time believed that the universe was divided into two competing realms, the kingdom of God and the kingdom of Satan, or the Devil. Satan was believed to seduce people into sin, which brought in its wake a loss of God's blessings of health and life. Paul said when sin came into the world, "death reigned" (Romans 5:14). But individual sinners were not always believed to be responsible for their own suffering. When evil befell them, ancient Christians and Jews suspected that someone- either Satan or a person who had sinned- was the cause. Hence Luke 13:16 speaks of a crippled woman as one "whom Satan bound for eighteen years."
John 9:2 voices the common assumption that sin leads to sickness: "who sinned, this man or his parents, that he was born blind?"
Healings, then, implied that the healed person was freed from the power of Satan and brought into God's kingdom, the realm of wholeness and life. Thus Jesus' miracles were seen as aggressive actions against Satan and his kingdom, even as they served to establish the kingdom of God (Matthew 12:28; Luke 11:20).
Ancient Judaism classified certain bodily defects (as well as corpses) as causing "uncleanness," which is displeasing to the perfect and holy God (Leviticus 11:44-45 21:18-20). Jesus' healings restored bodily wholeness: Such health was tantamount to spiritual holiness. A healed person, freed from his "unclean" defects, was now fit to be ritually purified. Thus the leper of Mark 1:44 healed by Jesus' touch was ordered to "Go. Show yourself to the priest, and offer for your cleansing what Moses commanded.' The demons which Jesus exorcises are fittingly described as "unclean spirits" (Mark 1:23,28; 3:11; 5:8,13; 6:7; 7:25); and so when "uncleanness" is expelled from a person, he is rendered "holy."
Being possessed by a demon, however, did not necessarily result in physical disease. It was thought that some demons, while not causing illness, were the cause of what we would now call mental disorders. Demons could thus enslave a person without actually making him ill. An exorcism was the cure for this second kind of possession. Thus Jesus directly confronted and cast out the unclean spirits. The first chapter of Mark relates how one of Jesus' first public actions was an exorcism. In this role, Jesus is characterized as the chief agent of God's kingdom; he is authorized with power to attack and despoil the kingdom of Satan.
At the time of Jesus, the Essenes were also teaching the people that cleanliness could be attained through an ascetic way of life. But in the eyes of his audience, Jesus surpassed these teachers because he "taught them as one who has authority, and not as the scribes." In other words, he was empowered to effect cleanness by expelling the "unclean" spirit. Yet his actions were challenged by his rivals, who argued that he was in league with Satan and was in fact acting as an agent of Satan: "And the scribes who came down from Jerusalem said, 'He is
possessed by Beelzebul, and by the prince of demons he casts out the demons.' " Jesus' reply to this charge, "How can Satan cast out Satan?" rests on the commonplace that allies do not war on each other.
Because the view of a dualistic universe was shared by many countries of the ancient world, exorcism stories are not confined to the Gospels. Similar tales occur in the other literature of the period. For example, in Book 8 of his monumental Antiquities of the Jews, the historian Flavius Josephus tells of an exorcist named Eleazar who cast demons out of a possessed person in the presence of the emperor Vespasian around 70 A.D., following magical procedures said to hark back to King Solomon. It is therefore not surprising that the evangelists shared with the wider culture at least some aspects of a common literary way of narrating an exorcism story. Such a narrative typically begins with an encounter between exorcist and possessed person; the severity of the disease is noted, after which the demon engages in defensive activity, such as magical use of the exorcist's name or pleas for leniency. The exorcist commands the demon to leave, demanding a visible sign that the demon is exiting; finally the crowd reacts with approval or fear.
