We know from Scripture that an individual can be possessed by a demon or demons (Matthew 4:24) but further questions abound within the church regarding this subject.

What Are Demons?

Demons are evil spirits in league with Satan. They have the power to enter and control certain human beings.

• Also known in the Bible as “unclean spirits” or “evil spirits”. They are associated with Satan, under his command (Luke 11:18). Thus they are most likely fallen angels who rebelled with Satan and shared his expulsion from heaven (Rev 12:9). They consistently oppose Jesus and the kingdom of God, but are completely subject to Jesus’ authority.
• Some humans can be controlled by demons. The Bible uses two expressions to describe this: “demonization” or “having a demon”. In such cases, the evil spirit gains some form of physical control over the human.
• The idea of “possession” comes from the fact that the demon takes up residence within the human and has much control over that individual.
• Demon possession is not temptation or any activity of an evil spirit outside of the human person.

Demons Want a Foothold

Demons will use any deception to have a person open that door. Any lie that is believed that is opposite the truth from God, whether conscious of it or not, can end up being a foothold. John 12:1-11, Ephesians 4:27.

• In New Testament cases where individuals are said to be demon possessed, an explanation of what caused them to be possessed is not given. For example: the man in a Capernaum synagogue (Mark 1:25-27; Luke 4:51-56), the Gadarene demoniac (Matthew 8:28-34, Mark 5:1-20, Luke 8:26-39), the demoniac boy (Matthew 17:14-21; Mark 9:14-29; Luke 9:37-42), or the slave girl at Phillippi (Acts 16:18). 
• However, scripture is not completely silent on this matter. John 12:1-11 tells us that even before Judas was offered money to turn over Jesus, he would help himself to what was put into the money bag. What started off small only grew. The Bible tells us that Satan entered Judas. It does not appear that Judas was aware of Satan entering him. 
• From this, and from scriptures like Ephesians 4:27 that states, “do not give the devil a foothold,” we can ascertain that demons can possess a person with or without them knowing; however, the person in one way or another has opened themselves up. 
• The term “foothold” or “gateway” is often used to describe this “opening up”. Many behaviors can be a gateway or allow a foothold by the enemy; involvement with new age, psychics, cults, drugs, the occult, witchcraft, spirit guides, rituals, passive meditation, sexual deviance, spells, oaths, “charged” teachings, and communicating with a spirit. 
• Demons will use any deception to have a person open that door. As with Judas, once the door is opened, it can grow into what can be called a “stronghold” where the enemy can begin to believe they have a right to take up residence. 

Demonic Manifestations

How do we know a person is demon possessed, and not dealing with a physical ailment or mental illness? Certain manifestations often indicate demon possession:

• Having instant knowledge and fear of the presence of Jesus
• Becoming sick or having a violent reaction to the presence of a Christian
• Making threats, weird noises, or utterances in counterfeit languages
• Yelling, cursing, or growling at others
• Demonstrating superhuman strength
• Being thrown on the ground
• Being stripped naked
• Many Christians want to know whether a Christian can be possessed by a demon. There is no question that Christians are involved in spiritual warfare. But demons have no authority or right to possess that which Christ owns. Because Christians have God the Holy Spirit living within them, it is not possible for a demonic spirit to take residence in the same space. 
• Yet Christians are still called to stay alert, be sober, stand firm (1 Peter 5; Colossians 4:2); to put on the whole armor of God (Ephesians 6:13); and to test and stay away from evil (1 Thessalonians 5:21-22). To do otherwise will only end up enslaving a Christian and grieving the Holy Spirit who is within them.

The Takeaway

It doesn’t take a priest with holy water to cast out a demon. Any believer in Jesus Christ can do it - but only because of the authority they have in Christ.

Ephesians 1:21-22 (NLT) Now [Christ] is far above any ruler or authority or power or leader or anything else—not only in this world but also in the world to come. God has put all things under the authority of Christ and has made him head over all things for the benefit of the church. 

• In Jesus’ day, the twelve disciples and the seventy cast out demons in Jesus’ name. Christians also did so in the book of Acts. In Luke 10:17, when the disciples returned, they declared, “Lord, even the demons are subject to us in Your name.” Jesus responded that He had given them authority over all the power of the enemy. 
• When casting out a demon there is no need to unnecessarily engage in conversation with the evil spirits. Simply announce your authority: “I am a believer in the Lord Jesus Christ who is God forever and I trust in Jesus and the blood of Christ. Jesus is my Lord and He has given me the right and authority to deal with you.” Then command the demons to come out in the name of Jesus Christ.” Demons can attempt to distract and may cause a scene on the way out. Because of this, be aware of who is around you. Pray for protection before and after. But never fear a demon and never back down. And don’t forget the ultimate goal of casting out a demon: the salvation of a soul.