Good verses... believers cannot be POSSESSED by the devil or his minions because God seals them (us) until the day of redemption and no man takes them away. Also, we are clothed in the righteousness of God, which would be impossible as demon possessed. There are a 100 verses or so about being sealed by God once we believe.
Ephesians 4:30 ESV
And do not grieve the Holy Spirit of God, by whom you were sealed for the day of redemption.
Ephesians 1:13 ESV /
In him you also, when you heard the word of truth, the gospel of your salvation, and believed in him, were sealed with the promised Holy Spirit,
Ephesians 1:13-14 ESV
In him you also, when you heard the word of truth, the gospel of your salvation, and believed in him, were sealed with the promised Holy Spirit, who is the guarantee of our inheritance until we acquire possession of it, to the praise of his glory.
Romans 8:9 ESV
You, however, are not in the flesh but in the Spirit, if in fact the Spirit of God dwells in you. Anyone who does not have the Spirit of Christ does not belong to him.
2 Corinthians 5:17 ESV
Therefore, if anyone is in Christ, he is a new creation. The old has passed away; behold, the new has come.
2 Corinthians 1:22 ESV
And who has also put his seal on us and given us his Spirit in our hearts as a guarantee.
Romans 8:16 ESV
The Spirit himself bears witness with our spirit that we are children of God,
Acts 2:38 ESV
And Peter said to them, “Repent and be baptized every one of you in the name of Jesus Christ for the forgiveness of your sins, and you will receive the gift of the Holy Spirit.
Acts 2:1-47 ESV
When the day of Pentecost arrived, they were all together in one place. And suddenly there came from heaven a sound like a mighty rushing wind, and it filled the entire house where they were sitting. And divided tongues as of fire appeared to them and rested on each one of them. And they were all filled with the Holy Spirit and began to speak in other tongues as the Spirit gave them utterance. Now there were dwelling in Jerusalem Jews, devout men from every nation under heaven. ...
Hebrews 2:10 ESV
For it was fitting that he, for whom and by whom all things exist, in bringing many sons to glory, should make the founder of their salvation perfect through suffering.
2 Timothy 2:19 ESV
But God's firm foundation stands, bearing this seal: “The Lord knows those who are his,” and, “Let everyone who names the name of the Lord depart from iniquity.”
Ephesians 1:1-23 ESV
Paul, an apostle of Christ Jesus by the will of God, To the saints who are in Ephesus, and are faithful in Christ Jesus: Grace to you and peace from God our Father and the Lord Jesus Christ. Blessed be the God and Father of our Lord Jesus Christ, who has blessed us in Christ with every spiritual blessing in the heavenly places, even as he chose us in him before the foundation of the world, that we should be holy and blameless before him. In love he predestined us for adoption as sons through Jesus Christ, according to the purpose of his will, ...
2 Corinthians 1:21-22 ESV
And it is God who establishes us with you in Christ, and has anointed us, and who has also put his seal on us and given us his Spirit in our hearts as a guarantee.