1. Their reality. Jesus knew the difference between a disease and a demon. Illness can sometimes look like demonisation (and vice-versa), but illnesses do not speak to those about to heal them! Nor do they possess supernatural knowledge! Just as their are good angels, so there are disobedient angels. These are demons, and their leader is Satan. The reality of demons, although not obvious to many Western Christians, is heavily documented in the literature of missions and revivals. And, in our own day, there would seem to be something more that superstition involved in at least some instances of astrology, ouija, fortune-telling, spiritism, witchcraft, and Satanism.
2. Their character. They are ‘unclean’. They are full of impurity and evil. To be demonised is an ugly caricature of what it means to be filled with the Holy Spirit. See 2 Cor 11:14.
3. Their activity. It is clear from Scripture that demons vary in their character and activities. A hierarchy of power is suggested by the phrase ‘principalities and powers’. Although it is true that ‘the whole world is in the power of the evil one (1 Jn 5:19), and human structures can be penetrated by Satan’s malign influence, sometimes, a demon can so control a vulnerable person that he is said to be ‘possessed by a demon’, or ‘demonised’. Demons seem to be particularly active in cultures as yet untouched by the gospel, and to be provoked by the coming of Christ – either in person, or in his gospel. Demonised people sometimes have unusual strength or abilities. They can mimic some of the gifts of the Holy Spirit such as tongues-speaking and healing.
4. Their knowledge. Demons, evil as they are, are not atheists, as many people claim to be. They know Christ, and are terrified of him, James 2:19.
5. Their conqueror. When Christ speaks, demons must obey. He refuses to accept the testimony of a demon. The method and effectiveness of his deliverance is in marked contrast to ordinary exorcists. They use magical charms and incantations, but he uses a simple authoritative word. Their deliverance is temporary, making room for re-possession later, but his is permanent, replacing the evil spirit with the Holy Spirit, and a life of unhappiness, confusion and destructiveness with a life of love, joy and peace. See Mt 25:41; 1 Pet 3:22; 1 Jn 3:8.
6. Their end. Geldenhuys notes that a final demonic onslaught may be expected at the end of the age in the Antichrist and his followers (2 Thess 2:9; Rev 13:2ff; 17:8ff. ‘But then also Christ will triumph and finally put and end to the evil one and all his powers of darkness (Rev 17:14)