Demonic possession, and Christians.
The Bible is clear that the Holy Spirit indwells a Christian. Since this is the case, a Christian cannot be possessed by a demon. God, and demons will not share a person. If you did cast a demon out of a lost person, their problem would persist, and be worse than it was before. After becoming free from the demon, it is possible that it would come back with more, so that the person’s condition would be even worse. The best solution for demoniacs, is to preach the gospel to them. If they repent, and believe, and are born again, then they are indwelt by the Holy Spirit. Their demonic possession will have ended, and God will put their mind in order. This isn’t to say a Christian cannot be tempted by demonic influence. It simply means they cannot be possessed by demons. As someone has already made clear, Satan is one created being. He is not omnipresent, omniscient, nor omnipotent. He does not possess aseity. He is bound by God in what he can do. After all, he is a creature, not the Creator. He is not God’s equal. He had to be permitted by God to do what he did to Job.
“In Him, you also, after listening to the word of truth, the gospel of your salvation—having also believed, you were sealed in Him with the Holy Spirit of promise, who is given as a pledge of our inheritance, unto the redemption of God’s own possession, to the praise of His glory.”
(Ephesians 1:13–14 Legacy Standard Bible)
““Now when the unclean spirit goes out of a man, it passes through waterless places seeking rest, and does not find it. “Then it says, ‘I will return to my house from which I came’; and when it comes, it finds it unoccupied, swept, and put in order. “Then it goes and takes along with it seven other spirits more wicked than itself, and they go in and live there; and the last state of that man becomes worse than the first. That is the way it will also be with this evil generation.””
(Matthew 12:43–45 Legacy Standard Bible)
“We know that no one who has been born of God sins; but He who was begotten of God keeps him, and the evil one does not touch him.”
(1 John 5:18 Legacy Standard Bible)
““And I will ask the Father, and He will give you another Advocate, that He may be with you forever; the Spirit of truth, whom the world cannot receive, because it does not see Him or know Him. You know Him because He abides with you and will be in you.”
(John 14:16–17 Legacy Standard Bible)
“You are from God, little children, and have overcome them; because greater is He who is in you than he who is in the world.”
(1 John 4:4 Legacy Standard Bible)