To be demon possessed means that a demon has direct control over what one does or says. A clear example of that is found in Luke 8. There we read about a man who lived in tombs and had unhuman strength. Jesus commands many evil spirits to leave the man, and he became normal.
Temple of the Holy Spirit
Every believer is a temple of the Holy Spirit. We are owned by God. Therefore it is clear that a demon can never own or possess us in that way. 1 John 4:10 teaches that “He who is within you (that is the Holy Spirit) is greater than he who is in the world” (that is the devil). In us is the Holy Spirit. In the world is the devil. And because the Holy Spirit is greater than the devil, the devil can never come into us to possess us. So make sure you are a child of God, and you may be sure no demon can ever possess you.
This does not mean that the devil is not dangerous to believers. Paul tells us that we must “stand against the schemes of the devil” (Ephesians 6:11). The devil may attack us by tempting us to sin (see also 1 Timothy 3:7). But faith, prayer, and the Word of God – these are parts of what is here called ‘the armor of God’ – will help us to resist the attacks of the devil. And when we resist, the Bible promises us the devil will give up: “Resist the devil, and he will flee from you” (James 4:7).
However, the devil remains a dangerous enemy. There are sins that give the devil a foothold in our life (Ephesians 4:27). If we turn from God, the hold of the devil over our lives can grow. Therefore in the Lord’s Prayer we pray “deliver us from evil” (Matthew 6:13), which probably means ‘deliver us from the evil one’, i.e. Satan. We pray for ourselves and for others that the devil will not get a place in our lives.
Deliver from evil
So we may pray that God will deliver us from the attacks of the devil. However, it is important to understand that these attacks are harassment coming from the outside. Our owner and possessor, who lives with his Holy Spirit in us, is God.