>>Our Western conception of the world is far too shallow. We don’t reckon with the spiritual realities that mark the world in which we live.
Western Civilization is all about Christianity. The problem is our Post-Western, Post-Christian world of moral and cultural absolutes. It is a world where secular powers have forced us to accept pagans and atheists as spiritual equals—or even as our spiritual superiors.
But in answer to the OP: No. A Christian cannot be possessed by a mere demon. But Satan sure can make one think he is.
>>The problem is our Post-Western, Post-Christian world of moral and cultural absolutes.
Oops. that should read:
The problem is our Post-Western, Post-Christian world of moral and cultural RELATIVISM.