I've always put it this way when describing it to people. If you are a Christian and believe in divine power, why would you not believe that there is also demonic powers that have influence as well? All too often people look at the actions of Christians of the past through the eyes of the modern church, where you go sing some songs, listen to some shitty pop rock music, have a potluck of casseroles, and gossip. That was not the church or God Christians of the past believed in, and their lives were ruled by divine and satanic involvement at all levels.