When I was a kid and was told about Jesus having a chat with the devil in the desert, I took that as a lesson that you should confront evil and not be afraid of it. Engage evil in conversation, hear the devil's side of the story and decide for yourself. Talk to anyone suffering from paranoid delusions and you'll see where fear of evil gets you. Your lack of knowledge concerning Christianity's appropriation of other religions has already been addressed, so I'll leave that point. Suffice to say that religion is a business of evolution, not revelation. I like the Hasidic view of satan being an agent of God sent to test people. The Old Testament god was very different from the New Testament God. It reminds me of the kind of friend you had in school or college who was really wild, then you meet up with them years later and they've got a family, got a sensible job and given up drinking. Part of you is happy that they've matured, but part of you is disappointed that they've betrayed their old values.