It is true that when a Christian sins, it may be because he has yielded to temptation from an evil spirit. Yielding to the suggestion of an evil spirit, however, does not mean that the evil spirit himself is then able to come inside the believer. When we sin as Christians, we break our fellowship with God because we have disobeyed Him (see 1 John 1:5-6). We feel guilty. We have not, however, broken our relationship with Him, as we are still His children.
If we confess our sins, “He is faithful and righteous to forgive us our sins and cleanse us from all unrighteousness” (1 John 1:9). Then our fellowship with Him is restored. Notice John did not say that we needed to be cleansed from any indwelling demons when we are guilty of sin.
Every Christian is faced with daily temptations from the world, the flesh and the devil. Paul wrote that we do indeed have a struggle against various evil spirits (see Eph 6:12). Therefore, to some degree, every believer is harassed by demon spirits. That is normal, and it is our responsibility to resist the devil and demons by faith in God’s Word (see 1 Pet. 5:8-9). When we believe and act upon what God has said, that is resisting the devil.
For example, if Satan brings thoughts of depression, we should think on a scripture that counteracts depression, and obey God’s Word to “rejoice always” (1 Thes. 5:16) and “give thanks in everything” (1 Thes. 5:18). It is our responsibility to act upon God’s Word and replace Satan’s thoughts with God’s thoughts.
We must recognize that as free moral agents, we can think about whatever we want to think. If a believer continually chooses to listen and yield to the suggestions of evil spirits, he can certainly open his mind to being oppressed, which is simply a state of being more receptive to and more dominated by wrong thoughts. If he chooses to yield even more, he could become obsessed with a certain kind of wrong thinking, which is very rare for a Christian, but can occur. Yet even then, if the obsessed Christian desires to be free, all he needs to do is determine to think about and yield to God’s Words and resist the devil.
But could he ever become possessed? Only if he willfully decided, from his heart, without being pressured, to reject Christ and turn his back upon Him completely. Then, of course, he would no longer be a Christian[1] and thus potentially could become possessed—if he yielded himself all the more to the evil spirit that was oppressing him. But that is a far cry from the idea of opening the door for an evil spirit to inhabit you through committing one sin.
It is a fact that there is not a single example in the New Testament of any Christian being possessed by a demon. Nor is there any warning addressed to Christians about the dangerous possibility of their being inhabited by demons. Nor is there any instruction regarding how to cast out demons from fellow-Christians.
The truth is that as Christians, we don’t need demons cast out of us—what we need is to have our minds renewed upon the Word of God. That is scriptural. Paul wrote:
And do not be conformed to this world, but be transformed by the renewing of your mind, that you may prove what the will of God is, that which is good and acceptable and perfect (Rom. 12:2).
Once our minds have been cleansed of old thinking patterns and been renewed with the truth of God’s Word, we gain victory over sinful habits and live in a consistent Christ-like manner. The truth is what sets us free (John 8:32). We are transformed as we renew our minds, not as we have all the demons exorcised.
Why then are there so many Christians who testify that they have had a demon (or demons) cast out of them? One possibility is that they just imagined that they had a demon in them that has since been cast out. Many Christians are gullible and lack knowledge of God’s Word, and so they are easy prey for “ministers of deliverance” who psychologically manipulate people into thinking they have demons. Once people are convinced they have a demon living in them, they will naturally cooperate with anyone who appears confident of his ability to exorcise the demon.
Another real possibility is that such people who have had demons cast of out them were not true believers in Christ at the time of their deliverance, even though they thought they were believers. The modern gospel, which stands in stark contrast to the biblical gospel, has deceived many into thinking they are Christians even though they are indistinguishable from non-Christians and Jesus is not their Lord. In Scripture, we find that when people believed the gospel and were born again, demons that lived in them automatically came out (see Acts 8:5-7). Demons can’t possess people who are indwelt by the Holy Spirit, and the Holy Spirit indwells all people who are born again.
[1] Those who hold to the position of “once saved, always saved” will no doubt disagree. I would encourage them to read Rom. 11:22; 1 Cor. 15:1-2; Phil. 3:18-19; Col. 1:21-23 and Heb. 3:12-14, paying special attention to the word “if” whenever it is found.