Imagine for a moment that God exists. There is a perfectly good being. He loves us, not just in general, but each one of us. He loves you. He even loves me!
This would be good news.
The trouble, if you are a God of love, is the overwhelming nature of the divine presence. He is great and the power imbalance between His magnificence and our created nature is very great. God must allow us consent and so, though God is the most reasonable of beings, He must be hidden. If God were to reveal Himself as He is, then we would have no choice but to worship. Sacred Scriptures say this day will come, but you can see that if God loves us, then He must put that day off. He must allow us to choose freely while more than a little blinded to His full glory.
Devils are not so bound. They do not wish us to be good, to embrace truth, and love beauty. If they exist, that is what devils would do.
God longs to show us perfect reason, but must not due to His gentility. Devils long to confuse us. A devil might do party tricks, loud, obvious, manifestations, and then retreat just enough so that they obscure their existence. God cannot do this “trick.” If we think hard enough, we can see that God might, just might, be logically necessary. Once we consider Him, we might doubt Him, but we cannot dismiss Him. We must decide He is not, or probably is not, or mayhap might be, but. . .
God allows our doubt, but the failure of faith is hard. Most of us find that failure too hard to intellectually sustain and so we embrace a God that hides, best He can, but reveals Himself to us eventually. At the moment of our death, perhaps, God is as plain as is compatible with choosing and so God’s justice, mercy, and love is maintained. If you think about the good God, then something like this must be true if He exists.
A good God cannot bully us to love this side of death. The hiddeness of God is why we can believe in the goodness of God.
If demons were to exist, then confusion is their goal. They do not wish us to be sure of anything. A devil would hate science, because science seeks truth. A devil loathes revelation, because revelation shows us beauty we might otherwise miss. Instead, devils wish to give us nothing: not even a knowledge they exist. A devil might stir up trouble, moan and groan, but in the end cannot wish to give us anything good, true, or beautiful.
If a demon existed, they would make a big show, but retreat when the scientist or philosopher came to examine the evidence. The good God will let Anselm and a thousand critics argue about His existence using ever more sophisticated logic. A devil will shout that “I exist” and then retreat the moment reason comes calling.
Evil does not side with reason. God must shadow His greatness, but cannot fully. Demons hide their folly, because they are fools.
So it goes.