Yeah.. It's weird though. My point was if you're following the Devil, you're not a Christian, because to be a CHRISTian you follow Jesus CHRIST....
As for it being a part of Christianity, I believe Islam believes in the Devil and hell too. I don't know about Judaism. You never hear about Heaven or Hell in a synagogue. Just how to live life for God, because he created you and is full of both wrath and forgiveness... I never said it makes sense but He shows both all the time according to those three religions.