Okay, established, just by being a believer, you accept the Bible truths on the existence of the principalities of darkness. All the same, it is evident that God constantly arranges PR, as in Public Relations on this war to reveal the enemy on an ongoing basis because this is a dirty war by a dirty enemy.
God does so by setting up encounters for the sole sake to expose this demonic world as true. That is why sometimes people can find they have an appointment with evil, because that encounter will serve God a purpose to reveal the enemy, if not then, then later at God’s appointed time, and help wake people up they are being played by the enemy.
Therefore besides the Bible, your loving God provides Show-and-Tell, kind of like randomly here and there switching on the spotlight in a dark forest so you see it is truly full of creatures lurking, which your night blindness can falsely lull you to believe are not there. By being alerted to them, you once more properly put your guard up so you don’t get devoured.
The key to remember is God is all mighty, and has existence in total control. What occurs is part of his massive plan for the better good. The way God controlled Pharaoh’s ‘bad’ behavior in Exodus which set the stage to show God’s glory (Romans 9:17-18) is but one of many examples how God orchestrates events which may seem bad on the surface, as in Pharaoh’s stubbornness and unyielding attitude to let the Israelites go, but which proved to impart important lessons as a result of that negative experience for the better of humanity, using a brutal dictator as a key player. In Pharaoh’s case, his evil behavior built the stage for God to show himself as an all-powerful God, the real God, the only God, and the importance of absolute obedience to him for the safety of their lives.
Because the world is big and it is full of people who never will even see a certain book or film God inspired to be made, God arranges multiple encounters as that, to reach as many people as possible through a chain of ongoing witnesses.
As one of those witnesses, I can testify that demons exist, having had several experiences in my lifetime.
In the next chapter I will cover some of those experiences in order that you can hear from another such person, who has actually witnessed the reality of demons firsthand, understanding that I am but one of many such witnesses, each of us living lives totally independent of one another, throughout the world, the world now, not the world back in Jesus’ time to help scatter one of the schemes of the enemy that demon happenings only were confined to the days of Jesus, or were just concepts Christ spoke about, even though he was pretty literal when he talked about them.
"I have spoken to you of earthly things and you do not believe; how then will you believe if I speak of heavenly things?" —John 3:12, NIV