T say that Satan rules this world is to say that the Holy Spirit is subordinate to Satan. Isn’t that blasphemy?
That’s not what Jesus meant when he said Satan rules the world. We can see from Job that, as you say, Satan only can do what God allows him to do. Satan rules people that reject God’s rule. When people submit themselves to God’s rule, they become “in the world but not of the world.”
Leif Erikson made very good references to the Scripture regarding Satan’s power. However, I feel that those references are more reflective of what God allows Satan to do. That is, he’s allowed to tempt us and to fool us, but to rule as in having complete authority is not what I understand Scripture to be saying.
I agree that there’s temptation and deception. I definitely don’t think that the devil has “complete authority,” for he’s subservient to God. But we can also see that he can have a direct, real impact in the world, through people or other means. For instance, Jesus said to the Jews who were trying to kill him, once, “you always do the will of your father the devil.”
Humans who do Satan’s will are literally his material tools and servants in the world. They have submitted to his will through their own free wills, and thus have become his aids, rather as demons are, though obviously to a lesser extent, because their corruption is incomplete.
Diocletian clearly did Satan’s will when he initiated the worst persecution Christians have ever suffered, shortly before the Medieval Ages dawned.
Hitler clearly was also doing what Satan wanted. If the Jews who were trying to kill Jesus were always doing Satan’s will, as Jesus said, then certainly Hitler and many of the Nazis were. People can be, in the world, children of the light or children of the darkness, or people perhaps in the process of becoming one or the other.
But Satan can get people killed, or raped, or verbally abused or harassed. He can dominate and manipulate earthly politics. He can do this not only through the influence of demons, but also through the willing service of humans who freely submit (unknowingly) to the will of the devil. Satan can truly manipulate economic, political or military policies, as well as the religious or moral perspectives of billions of people that have yielded to his desires. He can give orders and see them done around the world, as I have no doubt he is doing in Darfur, just like any king could.
So Satan really is the ruler of this world. He is, because the world freely chooses to serve him. But servants of Christ are in the world, yet not of the world, and they are not bound to the power of the devil. As Jesus said, “I have given you power to trample on snakes and scorpions and all the powers of the enemy.” We belong to another kingdom, so Satan cannot rule our fates. He can only dominate people who choose him instead of God.