What’s the difference? How can you tell? Does Satan have a pointed tail, a red body, and carry a trident or pitchfork? All valid questions. Let me give this a shot.
I don’t recall if it was Tim Keller, or Greg Laurie, or some other person, who said the people of the middle ages knew Satan was a proud being. After all, he began as an angel of light named Lucifer (or Morning Star in Isaiah), and could very well have been one of the “angels who stood before the Lord,” which would put him on par with Michael and Gabriel, the only other two angels named in the Bible.
Anyway, back to Satan in the middle ages.
Being a proud (and evil) being, the best way to fight him was to lampoon him. So they depicted him as a comical entity, ridiculing him, making him look foolish. Hence the red skin, horns, and pitchfork. It was like a Halloween costume.
Of course, succeeding generations didn’t know this, so they didn’t take Satan seriously either, and people began to believe he didn’t exist.
If we look at the Bible, Satan is a smug, self-centered, fallen angel. A commentary I read on Job said that Satan’s lack of any honorific when addressing God (linked in “smug” above) was a deliberate insult. This contrasts with John the Revelator, who fell at the feet of an angel - an unnamed angel at that - who told John, “Dude! I’m just a messenger! Only God should get worship.” Okay, I paraphrased a bit.
The upshot is, Romans teaches we shouldn’t worship things (or beings) that were created. Only He is worthy of worship, because all the rest of creation will pass away, but His Words will never die.
It may be of interest that the universe was created with words. “Let there be light,” and there was light.
So how can you tell the difference? Satan is a deceiver - which is like a super-liar. The Bible teaches us that anyone who tries to teach us who does not acknowledge Jesus is God in the flesh is a deceiver.
SIDEBAR: If I claim I’m the Pope, that’s a lie. Refuting it is easy. If I claim I’m a licensed electrician, and you should trust me to rewire your house, that’s deception. I’ve done some wiring, and could probably fake it well enough to fool a lot of people.
So Satan and his minions have the goal of pulling people away from God using deception. That’s what he did in the Garden of Eden. “Did God really say that? ‘Cuz, ya know, it’s not true. You won’t die if you eat that.”
This contrasts with God calling Himself The Way, The Truth, The Life.
The way to tell the difference between an angel and a fallen angel is how they react to God.
Disdain? Demon. Adoration? Angel.
That’s pretty much how you can tell a true Christian, too. There are always those who claim to be Christian who do nothing to indicate the truth of it.
There will always be those among the faithful.
