Exactly what it says on the (dramatic) title.
We always hear about Biblically accurate angels: the burning wheels with tons of eyes, the strange looking creatures that sound like they come from the anime “Evangelion”, the cherubim with 4 faces, but I had a thought while watching The Exorcist: Believer (it was…not good for anyone wondering. At all. The disrespect Regan’s mom had towards Merrin and Karras after they died saving her daughter was baffling to listen to, especially…but i digress) a couple of days ago, specifically, if that’s how the demonically possessed are said to more or less act in the Judeo-Christian scriptures, or if they’re they completely different to what we see in movies and games. I’m guessing it’s more than likely the second one, right, but I’m curious about the details like the signs someone’s possessed, the demon’s endgoal, and what they look like, basically everything you can gimme to sate this curiosity or to send me on a rabbit hole, if you’d be so kind?
Due to the nature of how translation works, interpretation will always be inherent to it, especially when we can’t ask the original author for clarification. As for the church wanting the faithful to know more about demons, you could argue that is why they borrowed so much demonology from other sources. As for why it wasn’t included in the Bible itself, any answer will have to be heavily seasoned with speculation. It is important to remember, however, that the New Testament was not intended as a “how to get to heaven” or “how to avoid hell” guide. It was intended as telling the story of why you get to go to heaven in the first place (the Gospels) and letters discussing how to live faithfully. Plus Revelation.