Exodus 8:16-24
The finger of God both casts out demons as well as hardens hearts. The finger of God is another term for the Holy Spirit. The Ten Commandments were inscribed on 
tablets of stone with the finger of God (Exod 31:18), so as St. Paul says, the law is spiritual (Rom 7:14). The law reveals the guilt of sin. It increases the trespass. This is a necessary part of repentance, but it also works as a hardening against those who continue to serve their own sin. God’s Spirit works through his Word to kill and to make alive. Those who continue to resist his grace are hardened by the very Word they reject.
When God sent plagues on Egypt, he did so to bring the Egyptians to repentance. But God knew that Pharaoh would continue to resist his call to repentance, so he told Moses that he would harden Pharaoh’s heart. People, like Pharaoh, boast in their so-called freedom to reject God’s Word. But they don’t realize that their hardened hearts are actually punishments from God. The Word of the cross is foolishness to them. It is an aroma of death to them. And this is a sign of their own judgment. So it was when Jesus cast out demons by the finger of God. Some of the religious leaders accused him of casting out demons by Beelzebub, which means Lord of the flies. This is ironic since Jesus is the same Lord who sent flees and flies to invade Egypt. The hearts of the Jewish leaders were hardened against Christ when he used the finger of God — the Spirit of God — to cast out demons.
And we should keep this in mind at all times. God’s Word both saves as well as hardens. This should cause us to fear God. We should tremble at the very sound of his Word, because it is the power of eternal judgment and salvation, to give faith and to harden. We should also, therefore, have great confidence in the Word. Jesus says that those who keep it are blessed even more than his mother who bore the eternal Son of God in her womb. This Word has the power to condemn, but even more so does it have the power to save. It reveals to us our Savior who died to destroy the power of sin and the devil. God’s condemnation of the devil’s power is strong. But Christ’s salvation from Satan is stronger.