Satan has been the God of this world since Adam turned it over to him. He remains so until a period after Christ return. Christ called him the God of this world. Satan offered Jesus every kingdom of the world if he would bow, Jesus never said they weren't his to give. When death is destroyed the fullness of Christ redemption will be achieved. As long as Christians are still in this crooked and perverse nation (world) Christ hasn't returned. What is God waiting for? Ephesians says the fullness of times, until then there is a harvest to be brought in. We are the laborers together with God to bring that harvest in.