Can a Christian be indwelled by a demon? For example, when Jesus called Peter "Satan" in Matthew 16, did that indicate Peter was possessed by a demon or Satan?
In Matthew’s Gospel we read:
In this exchange, Jesus responded to Peter’s suggestion that He not go forward with the Father's plan to send His Son to die on the cross. Obviously, Peter didn't understand what he was saying, nevertheless Jesus rebuked Peter for tempting Him to disobey the Father. Jesus told Peter his advice furthered the desires and purposes of Satan rather than the Father.
By the context, we see that when Jesus said to Peter, “Get behind Me, Satan,” Jesus wasn’t literally addressing Peter as if Satan were resident in Peter’s body. Rather, Jesus was calling Peter Satan to teach Peter that his desires supported Satan's purposes. Perhaps also Jesus was indicating that Satan was behind the scenes influencing Peter’s thinking and words. In either case, Jesus meant that Peter was not speaking by the Spirit nor was He speaking in agreement with the word of God. Rather, Peter was echoing the words and purposes of Satan.
This example reminds us that believers can unknowingly support Satan's goals by living in our flesh and not by the Spirit. Furthermore, all people (whether believer or unbeliever) can be manipulated by Satan without necessarily requiring that a demon indwell a person. The enemy is very powerful, and his power includes tempting believers, delivering false teaching, and even influencing our thoughts and emotions in opposition to God.
None of these influences requires an indwelling. Scriptures say that every believer can be tempted by Satan or even taught by him. For example:
Finally, scripture teaches that once the Holy Spirit resides in our bodies (because of our faith in Jesus Christ), we are forever sealed by the Holy Spirit and no longer accessible to the enemy for indwelling:
Jesus was explaining that were God to free someone from demon possession yet not deliver saving faith, He would have done little to help them. As long as a person remains “unoccupied” by the absence of the Holy Spirit (which is the case for all unbelievers), then that person will be available to host the enemy’s agents. Only if a body becomes occupied (e.g., indwelled by the Holy Spirit) is that person safe from the enemy ever returning to set up a home in the body again.
By logical deduction, we must also conclude that once we become a Christian, we are no longer susceptible to demon possession, though the enemy can still tempt, deceive and influence us in negative ways when we live in the flesh and not in the Spirit.