ISIS is labelled as evil, barbaric, primitive and medieval, but that does not help us to understand it. This is important, because you cannot deal with what you do not understand.
They are people who believe their cause is so good that they are justified in doing evil. To understand them, we need to understand the cause that they believe is so good that they are willing to do evil to support it.
Some commentators suggest that they are only interested in death and receiving 40 virgins when they go to heaven. This is an unhelpful caricature.
Their real cause is Islam. Islam is not just another religion, it is a cause. Islam means “submission” or “obedience”. Their goal is that everything in the world must submit to Allah. Every person and thing must come under his control. This cause is seen as so good that they are justified in using evil to achieve it.
War against those who refuse to submit to Allah is justified, if they can be forced to submit and obey. Creating chaos amongst those who refuse to submit to Allah is a good strategy, because it might allow those who submit to Allah to get control and brings things into submission (Islam).
In a way, Christians have a similar goal. We believe that everything will eventually be brought into submission to Jesus. This is what “Jesus is Lord” means. Every knee shall bow to him.
However, there is a big difference. Christians (mostly) believe that people must not be forced to submit to Jesus. Instead, by receiving good news, they should freely choose to submit to him. Jesus wants people to serve him because they love him. He does not want his people using military or police force to make others serve him.
Unfortunately, the church has not always understood this. In the middle ages, the church used military and police power to force people to accept the authority of Jesus (often in reality by forcing them to submit to the authority of the church).
Strangely, many Christians would still like to do that. They want to use military force against those who will not submit to their standards. They want to use political power to force people to honour Jesus and do his will.
I am wary about any group that believes that are justified in using military force to support their cause and make people submit to their Gold. ISIS is dangerous, because this is what it is trying to do.
Many Christians scare me nearly as much, because they want to use military force to accomplish God’s purposes on earth.