Hello presidente
Your negativity tells me that you have not read any of these spiritual warfare books, nor read testimonies about Christians who have been involved in the occult.
It would depend on which book you are talking about. I have heard and read testimonies about people who had been involved in the occult. I don't see, Biblically, while being involved in the occult would make someone better at casting out demons. What matters is that God's grace works through them in that area. You might know of some people who are rather powerful at casting out demons who were involved in the occult, but you could also find people who were never involved in the occult who did the same thing.
Some of the books about people's past demonic experiences might be fiction. I've read some expose's on that. Since I didn't research the information myself, I cannot say for sure. There have been a couple of author's who others said wrote works that weren't authentic. I also read a book, almost two, from an author who, if her book was accurate, apparently got a lot of her ideas about demons from someone who was allegedly possessed herself, then took Bible verses out of context to back up these doctrines about demons. Some of the verses were used in ways that were obviously wrong, for example a verse about the body in the resurrection being used to argue for a 'spirit body' that can come out of someone's body and throw plates at someone. The books made Satan and demon seem so great and powerful and Christians so miniscule and weak.
I was writing about the 'spiritual warfare movement' stuff from the '80's and '90's that still goes on today. One of the books used cases to argue. Some western Christians had gone into India, also South America, etc. and commanded demonic principalities to come down, or whatever, and supposedly after that revivals broke out. I had dinner with an author who'd been a missionary to one of those regions. He said many Christians had been laboring and praying in that region for a long time, and these people happened to go through. After a revival broke out, these people who'd come through claimed the revival as a result of their so-called 'spiritual warfare.' I do believe in spiritual warfare, but I am very concerned about some of these practices. Jude 9 and the surrounding verses are good to look at.
But that isn't what we were talking about with deliverance.
I initially did not have any interest in such material until my mother told my about a Christian lady that recommended such reading because she had found them to be useful. I also decided to read these testimonies and also found them to be useful. It made me aware of things that I was doing, which were causing unnecessary problems in my life and helped me to better understand how the devil attacks Christians.
Imagine you had cancer. There are doctors who have PHDs in oncology and have been treating cancer patients for many years (during the years some patients survived and some patients died), but they themselves never got cancer. Then you have those have had cancer and were told by doctors who have PHDs in oncology that they would die from the cancer, but instead of dying, they amazed doctors by surviving and their cancer got cured and they continued to live for several more decades.
So if you had cancer, would you only consult the doctors only or would you also think of consulting those who are cancer saviors (who had had experience in cancer and overcame it).
The doctors represent pastors who have text book knowledge (the bible) about demons and have experience in dealing with them (sometimes they have helped Christians to get rid of them and sometimes they struggled to help). Christians who used to be satanist represent the cancer survivors, who were involved in Satanism and overcame satan from first-hand experience and escaped Satanism and demons.
I don't know if doctors who had had cancer would necessarily be better than those who have not. I can't find any examples of someone who cast out demons in the Bible who was demonized prior. It reminds me of the idea that you can't help someone with their marriage if you haven't ever been divorced-- which is probably not a good approach to finding someone to help you. Someone who's been divorced might be able to give good advice, but someone who's been married for 40 years and never divorced might be a better choice.
There might have been some in the church back then. You can probably find some real-life examples in modern times, but there are also those who hadn't been, who hadn't been involved in the occult. I don't see it as a key ingredient. People who cast out demons need the power of God to work through them in that way. They need faith in the name of Jesus and boldness. Also, it could be helpful to operate in the gift of discernment of spirits. I see no reason to think the Spirit only gives the gift to those who had an occult background.
So you being negative causes me to suspect that you have not read them and you should rather read them, then be negative from the onset about content you do not know about.
On the contrary, I've read some material that I found particularly unhelpful, but you are talking about people who've had experience with demons, and the books I was thinking of when I posted before are about commanding demons to come down out of the heavenlies and such. Some books are good. Some, not so much. It depends on the book.
And the information is from Christians and are not a revelation from demons. These books are in Christian book stores and are published by Christian publishers.
They are not demonic but tell us how to fight demons from those who have had first-hand experience.
It depends on which book you are talking about. Some are good. Some are best avoided. I'd say avoid Rebecca Brown books. I've heard Lester Summerall's book on casting out demons highly recommended. But I haven't been able to finish it. I read parts of it when I was at a library overseas, but I was not able to check out books.