Demons are those spirit beings which oppose the work of God. They are under the direction of Satan, with whom they rebelled against the authority of God (Revelation 12:3-4). At times they are called “unclean spirits” (Matthew 10:1), or “evil spirits” (Luke 7:21). Mention is made of them over 100 times in the New Testament.
Possessors of great strength (Mark 5:3; Acts 19:16), demons are intelligent beings with emotions, wills, and individual personalities. Yet they are limited creatures, unable to be everywhere at once. Satan, also a limited being, extends his power greatly through his control of demons. However, at times, God uses them to further His own purposes. For example, God used an evil spirit to punish King Saul (1 Samuel 16:14), and to keep the Apostle Paul humble (2 Corinthians 12:7).
These evil creatures promote the Devil’s counterfeit substitutes for real Christianity. Idol worship finds its source in demon activity, and false religions which promote works righteousness or licentiousness are the work of the dark world (1 Timothy 4:1). Demons can inflict disease (Matthew 9:33; 12:22) and mental disorders (Mark 5:4-5). But note that not all disease or disorders are the result of demon workings. Demon activity is often connected with extreme immorality (Deuteronomy 18:9-14; Revelation 2:20-24).
At times demons can enter into or possess a human being, and this is the opposite of being filled with the Holy Spirit. Usually this occurs when a person has willfully turned against God and turned to Satan. Demon possession manifests itself in extreme or unusual behavior, and often results in self-destroying actions (Matthew 17:15; Mark 5:2-5). Demon oppression, or the exercise of evil power, can happen when people subject themselves to demonic influences such as astrology, seances, witchcraft, ouija boards, tarot cards and other kinds of fortune telling.
Demons are Satan’s agents in the intense spiritual struggle between good and evil. However, Bible believers know that the war against these wicked ones was won at Calvary and the Tomb. 1 John 4:4 reminds us that we have overcome them, because the one who lives in us (Jesus Christ), is greater than the one who is in the world (Satan).