@KarlGessler I think this is a good question. I know some believers say because we have the Holy Spirit dwelling in us we can't at the same time be indwelt by a demon. Some of the early church fathers however seemed to believe Christians could have demons. However I believe Jessi penn-Lewis and Watchman Nee give good evidence that a true Christian can be demon possessed or at least influenced. Since the Holy Spirit dwells in our human spirit and not our soul but instead we are too be filled with the Spirit, then it follows that the soul can be a war ground between the devil and Holy Spirit. Are we to give ourselves to the Lord or parts of our life to the devil? Of course demonic influence and possession are not the same and so it's a little more complex but I do believe true Christians can be possessed but not to the same degree as unbelievers. Of course this study can be alot more detailed but this is my two cents worth.