power struggle

In class on Wednesday we talked about the very limited power of demons described in The Screwtape Letters and the contrast found in Frank Peretti’s book, This Present Darkness, where demons seem to have almost equal power as angels over the people and events of this world. I wonder which depiction is more accurate. We know from Revelations that God has the ultimate authority in heaven and on earth, but how much power earthly power does he allow Satan to have here and now? I am reminded on Ephesians 6:12 which says, “For our struggle is not against flesh and blood, but against the rulers, against the authorities, against the powers of this dark world and against the spiritual forces of evil in the heavenly realm.” This verse makes it sound like Satan does have a considerable amount of power, but at the same time, Christ tells his disciples in Matthew 28:18, “All authority in heaven and on earth has been given to me.” I guess it’s just weird to me to think that there is a balance of power on this earth between good and evil, but at the same time, evil only has power because God allows it to have power.