Question: "What does the Bible say about demon possession / demonic possession?"
Answer: The Bible gives some examples of people being possessed or influenced by demons. From these we can find some symptoms of demonic influence as well as gain insights as to how a demon possesses someone. Here are some of biblical passages: Matthew 9:32-33; 12:22; 17:18; Mark 5:1-20; 7:26-30; Luke 4:33-36; Luke 22:3; Acts 16:16-18. In some of these passages, the demon possession causes physical ailments, such as inability to speak, epileptic symptoms, blindness, etc. In other cases, it causes the individual to do evil, Judas being the main example. In Acts 16:16-18 the spirit apparently gives a slave girl some ability to know things beyond her own learning. In the case of the demoniac of the Gadarenes who was possessed by a multitude of demons, he had superhuman strength, went around naked, and lived among the tombstones. King Saul, after rebelling against the LORD, was allowed to be troubled by an evil spirit (1 Samuel 16:14-15; 18:10-11; 19:9-10) with the apparent effect of a depressed mood and an increased desire and readiness to kill David.
Thus, there is a wide variety of possible symptoms of demon possession, such as a physical impairment that cannot be attributed to an actual physiological problem, personality changes such as major depression or uncharacteristic aggression, supernatural strength, a disregard for modesty or “normal” social interaction, and perhaps the ability to share information that one has no natural way of knowing. It is important to note that nearly all, if not all, of these characteristics may have other explanations, so it is important not to label every depressed person or epileptic individual as demon possessed. On the other hand, I think that in our western culture, we probably don’t take Satanic involvement in people’s lives seriously enough.
In addition to these physical or emotional distinctions, one can also look at spiritual attributes as showing demonic influence. These may include a refusal to forgive (2 Corinthians 2:10-11) and the belief in and spread of false doctrine, especially concerning Jesus Christ and His atoning work (2 Corinthians 11:3-4,13-15; 1 Timothy 4:1-5; 1 John 4:1-3).
Concerning the involvement of demons in the lives of Christians, the apostle Peter is an illustration of the fact that a believer can be INFLUENCED by the devil (Matthew 16:23). Some refer to Christians who are under a STRONG demonic influence as being “demonized,” but never is there an example in Scripture of a believer in Christ being POSSESSED by a demon, and most theologians believe that a Christian CANNOT be possessed because he has the Holy Spirit abiding within (2 Corinthians 1:22; 5:5; 1 Corinthians 6:19).
We are not told exactly how one opens himself up for possession. If Judas’ case is representative, he opened his heart to evil (in his case by his greed - John 12:6). So it may be possible that if one allows his heart to be ruled by some habitual sin...it becomes an invitation for a demon to enter in. From missionary experiences, demon possession also seems to be related to the worship of heathen idols and the possession of occult materials. Scripture repeatedly relates idol worship with the actual worship of demons (Leviticus 17:7; Deuteronomy 32:17; Psalm 106:37; 1 Corinthians 10:20), so it should not be surprising that involvement with those religions and practices associated with those religions could lead to demon possession.
Thus, it is my belief based on the above Scriptural passages as well as some of the experiences of missionaries that many people open their lives up to demon involvement through the embracing of some sin or through cultic involvement (both knowingly and unknowingly). Examples may include immorality; drug/alcohol abuse...as these alter one’s state of consciousness; rebellion; bitterness; transcendental meditation. In our western culture, we see an increase of eastern religious teachings under the guise of the new age movement.
There is something that must not be forgotten. Satan and his evil host cannot do anything the Lord does not allow them to do (Job 1,2). And this being the case, Satan, thinking he is accomplishing his own purposes, is actually accomplishing God’s good purposes...even as in the case of Judas’ betrayal. Some people develop an unhealthy fascination with the occult and demonic activity. This is unwise and unbiblical. If we pursue God with our lives and are clothing ourselves with His armor and relying upon His strength (not our own) (Ephesians 6:10-18), we have nothing to fear from the evil ones, for God rules over all!