Non-Christians can have demons in them, Born Again Christians can only have demons on them (I believe), because the enemy cannot reside side-by-side with the Holy Spirit.
If demons are cast out or off someone, and there is no understanding of the Bible or teaching, the enemy can come back with seven more (Luke 11:26, Matt 12:45).
Going back to Christians and non-Christians, satan operates in a similar fashion to prayer as we understand it. Even Islam simply requires someone to recite the shahada to become Muslim. He wants individuals to speak ‘things’ into being in their own lives. Things like lies! Lies about ourselves, lies about other people, lies about God, you name it, any lie will do. As long as it goes against God or separates us from God. Once things have been spoken into our lives, he prompts us to act them out. Things like fighting, cursing, swearing even killing. Out of the abundance of the heart, the mouth speaks (Matt 12:34).
Don't fall in to the trap that many people do, thinking that behind every door there is a supernatural event; that each time you pray you expect God to perform for you. That's not going to happen.
Take a minute to imagine what would happen if God granted everyone's prayers! It would be chaos! I believe that to maintain the order of things there are most definitely miracles and most definitely miraculous healing, but when it comes to personal requests, this is where we have to understand why it is so important that we allow God to change us in order that we can 'perform' the necessry task.
We are the supernatural event we've been waiting to happen. We are the individuals that have been born again, we are the ones the Holy Spirit has chosen to reside in. Therefore we have to understand how the order of prayer and Christian life operates and not to become disillusioned that God isn't answering our prayers.
Lest we forget, we have a new destiny in heaven once we've finished our training here on earth. We're going home. Therefore we can look to enjoy this time on earth. But consider this. What type of person would God want in heaven? An aggressive entrepreneur who makes loads of money for himself and despises everyone or someone who wants to help others? I'll leave it to you to decide, but we don't need money in heaven!
Many people pray for Jesus to heal - for him to perform whichever actual duties are required. Sadly, this is a form of unbelief, a misguided understanding of what Jesus did for us on the cross. This is a lie of the enemy, satan.
Asking Jesus to act on our behalf is asking him to be crucified again, it’s like saying what He did for us was not enough so get back on the cross and die for us all over again. When He died, He said “It is finished” and at the point of His resurrection He gave us back the authority to do even greater things than He (See John 14:12).
We must understand our authority as born again Christians, as individuals who believe that Jesus is the son of God and Lord of our lives, that we repent of our sins and are baptised in water. See John 3:1-5.
Baptism isn’t an option, it isn’t about being part of a sect, faction or out of personal choice. It is fundamental to being a Christian. There is no argument Jesus says we must be baptised to be born again. Jesus said it and that’s good enough for me.
Non-Christians; satan is not really bothered with this group because they will already do what he wants and they’re not following God, Jesus or the Holy Spirit and so they’re no threat. They will do what pleases them without taking any notice of The Bible or believing that there’s any consequences for their actions.
Religious groups like Islam will kill them all the same because they don’t believe in ‘their’ god, but none of the other religious groups are bothered about non-believers.
Christians; this group have already confirmed their allegiance to Jesus and therefore they have the power of the Holy Spirit in them to act on and receive from direction from God. This is why satan makes a bee-line for Christians, via Islam, left-wing politics and any other faction that can silence the Christian faith.
Satan will do everything he can to turn a Christian away from God, even the smallest thing can act as a doorway to being tempted even more. Just one cigarette, just one drink, just one joint, just one look at porn. One thing can lead to another and we must be on our guard. But also misguided thinking about faith in operation. This is why we have to study and meet together to ensure we are all on the right track.
We are told to pray without ceasing (1 Thessalonians 5:17) for good reason. Don't let your guard down.