I don't think there is such a thing. I think the existence of demons would prove the existence of god. For me, I would welcome an experience where I saw demons because that would answer my questions. Maybe they're hiding from me because they know this.-lol IMO this is another thing that humans have made up to explain the unexplainable.
When God or Satan reveals there-self to me I will believe. Imperfect men are the only testament to both of these ideas and that is not good enough for me. When people will say "You have to have faith" it bothers me because what am I having faith in? My faith would be faith in men not god. Having faith in a person whom I've never met or have no real proof of is not I wise decision to me.
The bible says the writers were inspired by god. But the writers wrote that. Of course that is what they'll say to drive home the point and so you won't question. I don't put anything past anyone no matter how long ago they lived.
I believe what they wrote was their best explanation of what they have seen and heard. Plenty of people have said plenty of things to explain why. At one time people believed the earth was on a turtles back! Why is this not true? What if it was in the Bible? Oh, is that silly? Am I comparing apples and oranges? Is that any different from believing a man parted a sea or a man gathered up EVERY animal and restarted the Earth? What about the Polar Bears and Penguins? That sounds silly to me. Think about the stories in the bible and you'll see.
So, no I don't believe there are invisible men who float around and worry who we worship. Call me crazy I guess.
