Believers have God’s spirit inside of them because they were made pure by the sacrifice of Jesus. They don’t need to be in a ritually clean state to enter God’s presence in a building in Israel anymore, because we are the building (temple). Paul says our bodies are the new temple in 1 Cor 3:16-17, 1 Cor 6:19-20 , & 2 Cor 6:15-18. And the Holy Spirit is only available to those who received Jesus as Lord (John 14:15-17, Rom 8:5-11). So how can an unclean spirit ever enter this “new temple” which is the body of a believer?
The Holy Spirit had its first new covenant appearance in Acts 2, and it was described as wind and fire just like God’s presence described in the old testament. The same flaming twister that was in the wilderness (Num 9:15-23), fire burning the burning bush (Ex 3:1-5), the blaze on Mt Sinai (Ex19:16-20), and the illuminated presence of God in the Tabernacle hovering above the Ark of the Covenant (Num 7:89, Lev 16:11-13), is the holy spirit. In the old covenant, the fiery presence of God would destroy anyone who wasn’t anointed or ceremonially pure enough to enter his presence (Lev 10:1-7, Num 16:16-35). Now under this new covenant, that presence is now inside of believers, to help them overcome sin nature. That’s why in Acts 2, smoke and fire appeared. God poured his spirit out on humanity as promised in Joel 2:28-32, and transformed the hearts of his people as Moses prophesied in Deuteronomy 30:6 and Ezekiel in Ez 36:22-27.
When Jesus cast out the demon in Matt 12:22-37, he is criticized by the Pharisees as using the power of Satan, because he can cast them out so effectively. Jesus replied that it doesn’t make any sense for him to use Satan’s power to fight Satan’s kingdom. He asks them where they think their own exorcist get their power from? He says his power to cast out demons comes from the Spirit of God which proves he is of the Kingdom of God. In verse 29, he sums up what is saying with this, “For who is powerful enough to enter the house of a strong man and plunder his goods? Only someone even stronger—someone who could tie him up and then plunder his house.” The “house” he is referring to in verse 29, is a person’s body and it is demons that enter human bodies and wreak havoc in this context. The only one that can remove a demon is the “stronger man” aka the Holy Spirit. Then he talks about what happens after an exorcism that doesn’t involve the holy spirit in verses 43-45 of the same chapter. He says, “When an evil spirit leaves a person, it goes into the desert, seeking rest but finding none. Then it says, ‘I will return to the person I came from.’ So it returns and finds its former home empty, swept, and in order. Then the spirit finds seven other spirits more evil than itself, and they all enter the person and live there. And so that person is worse off than before. That will be the experience of this evil generation.” We all need the “stronger man” to come in, kick unclean spirits out and stay there so that they can never come back. Believers have the holy spirit and once a person gets saved they cannot be possessed by demons.
One last note, in the old covenant, the people had to be ritually pure to come to God’s presence at the Tabernacle/Temple. This meant that God’s presence was so holy that the people had to double-check if they touched a dead body, an unclean person, were menstruating, or had sex recently. If the Israelites couldn’t go near God’s Tabernacle/Temple, in an unclean state, then what makes anyone think that an unclean spirit can go anywhere near the Tabernacle/Temple? Furthermore, if believers are the “New Temple” then no unclean spirit can inhabit their bodies. This idea of believers needing “deliverance” in every church service is bad theology because it denies the power of the holy spirit. It’s people who are unsaved that need deliverance and receiving Jesus and the Holy Spirit is by itself deliverance.
Some people believe that every sinful temptation is a demon but the Bible doesn’t teach that because sin existed before demons. I believe demons come from the Nephilim and the Giants from Genesis 6. More on the here. However, Cain murdered his brother Abel because of his own sinful desires. James chapter 1:14 does that sin comes from our fleshly desires not unclean spirits.
Believers in the book of Acts exorcised demons out of unbelievers who are possessed. For believers, demons can attack from the outside and that is something we pray for each other about. You noticed in the Bible that healing and demonic exorcism are two separate things (Matt 4:24, Matt 10:8) which mean not all sickness and disease come from demons either. In fact, the symptoms of having a demon always involve some kind of neurological problem. Like the woman with the back problem in Luke 13:16, or the boy with seizures that require fasting and prayer (Mark 9:14-29). Other kinds of physical illnesses like bleeding issues, broken limbs, or leprosy were simply sicknesses and not demons.
Lastly, some people suggest that there are physical signs of an exorcism that come along with deliverance like sneezing, yawning, or vomiting. None of the exorcisms in the Gospels or the book of Acts included sneezing, yawning, or vomiting, so none of that related to what Jesus was doing. The only old testament exorcism we see is David playing the harp and soothing King Saul (1 Sam 16:13-23). There is one mention of sneezing in the bible when Elisha raised the widow’s son from the dead (2 Kings 4:35). The boy sneezed seven times when he was revived, but that was a resurrection, not an exorcism, why would seven demons be sitting on a dead body? No resurrection in the rest of the bible old or new testament mentions sneezing or demons. Besides, before the boy died, he had a major headache (2 Kings 4:19), so as far as we know sneezing could have been the body discharging a remnant of a tumor or growth that was destroyed when Elisha revived him. These ideas are commonly taught in certain circles but it’s not consistent with what is written, so I don’t see them as necessary to believe. Exorcism in the Gospels and in Acts involved the holy spirit so ritualistic tools like holy water, cross symbols, and such were not involved, likewise, the only physical sign of a demon leaving was screaming not sneezing, yawning, or vomiting. Jesus and his followers just gave a command to leave with the backing of the holy spirit (Mark 1:21-28, Mark 3:11-12, Mark 5:1-20, Mark 6:7, Mark 7:29-30, Mark 16:16-18, Luke 4:33-37, Luke 10:17-20, Luke 13:10-13, Matt 10:1, Acts 5:16, Acts 8:17, Acts 16:16-21, Acts 19:11-12).
If Christians could be possessed they wouldn’t be able to pray to God, they would mindless slaves like the men with the legion in Matthew 8:28-34 or the women in Acts 16:16-18. Demonic oppression involves torment. They can cause certain kinds of stress and anxiety. But that’s not the same as someone whose mind is being controlled by a demon 100%. The Holy Spirit is already inside of a believer and they are living temples, so that prevents a believer from being possessed.
Ephesians 6:10 A final word: Be strong in the Lord and in his mighty power. 11 Put on all of God’s armor so that you will be able to stand firm against all strategies of the devil. 12 For we are not fighting against flesh-and-blood enemies, but against evil rulers and authorities of the unseen world, against mighty powers in this dark world, and against evil spirits in the heavenly places.