How are Yahweh and Allah different?
God has the right to kill anybody he wants. In fact, he is responsible for all death. "The Lord gives and the Lord takes away; blessed be the name of the Lord" (Job 1:21).
We don't own our lives. God owns our lives. He made them, and he has the right to do with them as he pleases.
The question becomes: When he uses a human to kill another human, what are we to think?
There is an overlap between the way Muslims think about God and the way Christians think about God in the Old Testament. Clearly God appointed that Joshua would go into the promised land and destroy the inhabitants. And the reason he commanded it, as stated in Deuteronomy 9:4, is that they were greatly wicked:
Do not say in your heart, after the Lord your God has thrust them out before you, "It is because of my righteousness that the Lord has brought me in to possess this land," whereas it is because of the wickedness of these nations that the Lord is driving them out before you.
Even back in Genesis, when God promised the land to Abraham, he said that his offspring would first go down to Egypt and spend 400 years there because the iniquity of the Amorites was not yet complete (15:13-16).
So God was giving more and more time, and the pagans in the land were filling up more and more sin in resistance to God's common grace. Then the time came for their judgment, and he used the people of Israel to judge them by appointing them to go in to kill.
That is what I believe, and if the Muslims agree that Allah has worked that way too, then I acknowledge the overlap.
The difference now is that, with the coming of Jesus Christ, God does not relate to people like that anymore. Back then the people of God were a theocratic, ethnic, and political entity. Today they are not. With the coming of Jesus Christ, the Kingdom has been taken away from the people of Israel and given to a people bearing its fruits, namely, the Church.
The Church is a people gathered from all tongues, tribes, peoples, and nations. Jesus Christ himself has borne our sins, and he sends us out to preach a gospel of grace and of the forgiveness of sins, based on his death. What unites us now are not our political and ethnic realities but, rather, our faith in Jesus Christ.
So we're not building an earthly kingdom. We're not protecting an ethnic entity. In the name of a crucified Savior we are gathering people from all nations, a people who are called to love their enemies and even die for them.
Christians now spread the gospel by suffering and dying, not by killing. So a change has happened. And there's the big difference.
Muslims don't have a savior. They don't have Christ. They don't have a means of forgiveness. They simply have an authoritative God who says, "Do this and don't do that." And they just have to wait until judgment day to see whether they have been good enough to enter heaven. And they still believe that their God can authorize his people to kill infidels.
So today there is a huge difference between Christianity—as Christ has defined it for us—and Islam. Not only do they not have a savior, they neither have a God who calls them to suffer and die and spend themselves in sacrifice for the lost.
Pilate asked Jesus, "So then you are a king?," and he responded, "My kingdom is not of this world. If my kingdom were of this world, my disciples would have been fighting" (John 18:36). That is huge to me, because it says that we don't fight to establish God's kingdom. We do not take up arms.
Bullets and bombs is not how Christianity spreads. And the reason for that is that Christianity is a faith where people must put their belief in Jesus without coercion. You can't put a gun to somebody's head or a sword to their throat and make them a Christian. Islam, however, as I understand it, believes that you can subdue people and make them do the Five Pillars. If they are outwardly willing to do them, then they qualify.
Christianity is a radically different thing. We have to voluntarily renounce sin and embrace Jesus as our substitute sacrifice and substitute righteousness. And when we do that, we are justified and given an eternal inheritance in heaven. And it is out of that hope that we lay our lives down for other people and spread the gospel that way, not by killing.