I have a vivid childhood memory of sitting in my bedroom and singing anti-Satan songs with my sister. We were both the composers and lyricists of these songs which they revolved around words that we normally were not allowed to use. So we danced around my bedroom singing, "Satan, you're so stupid," and, "The devil is dumb."
Apparently my mother heard us from the hallway and popped her head through the door.
"What are you girls doing?"
"We're singing songs about how bad Satan is." We responded.
My very smart mother took a moment to think before replying, "Don't you think Satan would like it even less if you were singing about how great Jesus was? Why spend your time focusing on Satan when you could be focusing on God?"
She left the room and we began singing again, making up new lyrics as we went along.
I was treating the devil as if he were an equal and opposing force of God--God's opponent in a cosmic arm-wrestling match that would only be resolved at the end of time. It wasn't that I was taking the devil too seriously...it was that I was not taking God serious enough.
I was reminded of the above story when I came across this advice from Karl Barth:
"Everyone who has to contend with unbelief should be advised that he ought not to take his own unbelief too seriously. Only faith is to be taken seriously; and if we have faith as a grain of mustard seed, that suffices for the devil to have lost his game." (Barth, Dogmatics in Outline, pp.20-21.)
I find these thoughts very comforting. The doubts I may encounter in my spiritual journey deserve attention, but the gravity of my doubt, no matter how large it may seem, pales in comparison to even a tiny grain of faith.