I have read books by Christians who offer insights on demons that go way beyond Scripture. Usually this is based on personal experiences. Some have gotten a good deal of “information” from being present at exorcisms.

To those wishing to explore a biblical perspective on demonic nature and activity, as well as spiritual warfare, Randy recommends these books: 3 Crucial Questions about Spiritual Warfare, by Clinton Arnold (Baker Books, 1997). Lord Foulgrin’s Letters, by Randy Alcorn

Satan is so delusional that, in his blinding hatred opposing God, he willingly fulfills God’s decree as it is plainly revealed and known by him.

It is unthinkable to me that God would allow one of His children, whom He purchased with the blood of Christ (1Peter 1:18-19) and made into a new creation (2Cor 5:17) — to be possessed and controlled by a demon.  

This is a question and answer concerning prayer and angelic warfare portrayed in Randy Alcorn's books Deadline, Dominion and Edge of Eternity.

Originally I intended the following to be the Introduction to Lord Foulgrin's Letters. Later I decided to shift it to the back of the book, realizing some readers would want to dive straight into the story without explanation.

I've been wanting to ask you a question for a long time now. In your work, you make it clear that you don't believe that Satan can read our thoughts. 

The principle of authority is that we are in the kingdom of Christ. Jesus is Lord and head of all power and author­ity. Satan has absolutely no legitimate authority over the believer.