The enemy is at war with the saints (Re 13:7); we’re in a continuous spiritual battle. (Ep 6:11-12) The basic dynamic in this war isn’t what I was taught, and it’s quite simple: wrong beliefs give the enemy spiritual ground (2Ti 2:25-26), believing the truth takes it back. (Jn 8:32)
The enemy’d have us believe there’s a LOT more to it than this, but he’s the father of lies (Jn 8:44), so why listen to him?
Think of spiritual ground as territory in our minds and hearts defined by our beliefs. The enemy has jurisdiction wherever we’re holding a lie (Ep 4:27); it gives him access to influence our thought patterns, motives, emotions and will to bring us into bondage, alienate us from God, and destroy us. This ground is called a carnal mind (Ro 8:7-8), the flesh (Ga 5:17), and our old man. (Ep 4:22)
Repentance is replacing lies with truth (2Ti 2:25); it recaptures spiritual ground and sets us free. (2Ti 2:26)
Getting hold of this changes everything. Wrong beliefs produce wrong attitudes, motives, and actions which alienate us from God and create spiritual, mental, emotional and physical bondage in our lives. (Ja 1:13-16) Truth then becomes infinitely precious: we buy the truth and sell it not (Pr 23:23); we seek it out, obey it and never let it go; it’s the key to freedom. (Ep 6:14)
In warring against us, the enemy is relentless in presenting lies to us in various forms: wrong teaching, emotional impulse, physical and emotional trauma, all with the purpose of gaining more ground, more control in our lives to destroy us. (Jn 10:10) This is how he works in the children of disobedience, who accept his suggestions as their own and act on them. (Ep 2:2) It’s how we all started out. (Ep 2:3)
To maintain the ground he already has, the enemy protects it with strongholds, irrational emotional ties to deception, moving us to feel comfort, pleasure, safety and security in our lies (Pr 9:17), and to feel deeply threatened by any challenge to them. (Ge 19:9) He does this because he has no other defense; lies cannot be upheld with a divine moral standard or with truth, only by other lies and our emotional attachments to these lies. They’re easy to spot: intense and intrinsically irrational, rooted in and springing from an innate hatred of God and His Law. (Ps 2:1-3)
No challenge to a belief threatens our well being: when an idea makes us feel defensive or fearful we have a stronghold guarded by the enemy. To love the truth, to be earnestly seeking it out wherever we can find it, and constantly shining the light of God’s moral standard, Torah (1Jn 3:4), on all of our beliefs and attitudes so that we might be fully aligned with Him throughout our entire being (1Jn 3:3), is to expose and disable all our enemy strongholds. (2Co 10:3-5)
Then, taking the sword of the Spirit, as God gives us understanding, repentance and faith, we may freely and relentlessly expose enemy ground and take it back (2Th 2:13), gaining progressively more and more freedom in our spiritual lives. (Ps 119:45)
The ground of the enemy in our lives can take many forms; in extreme cases it can include complete control of our bodies (demon possession). It’s all on a spectrum of infestation and control, but the principles are the same.
Casting out demons is God breaking demonic control, overriding their ground, and expelling them from a person’s body. Generally, this seems to be to restore the victim’s full use of their facilities so they can repent, seek God, and properly care for their bodies. But if there isn’t sincere repentance after the exorcism, demonic influence in the mind and heart will persist and the physical invasion may return and be much worse.
“When the unclean spirit is gone out of a man, he walketh through dry places, seeking rest; and finding none, he saith, I will return unto my house whence I came out. And when he cometh, he findeth it swept and garnished. Then goeth he, and taketh to him seven other spirits more wicked than himself; and they enter in, and dwell there: and the last state of that man is worse than the first.” (Lk 11:24-26)
Jesse Penn Lewis’s classic, ground breaking work, War on the Saints, is, I think, a good read. The full text is on line and it’s free. Her thesis is: “passivity of the mind is the chief basis of (demon) possession.” Much of my thinking was initially motivated and encouraged by her work. She wrote, along with Evan Roberts, to explain the infiltration and destruction of the Welsh revival, the last, large-scale move of God in our era of which I am aware.