Why doesnt God just eliminate Satan?

There is a reason for everything. How can you say something is good without knowing what bad is? Therefore, there must be Satan if there is God. How is it possible to know what temptation is without being tempted? I believe that without having the opposite of something, one will never truly appreciate the good in something. We may not know what God has in store for us, but he has a plan. It may seem like there is no plan or reason for certain things to occur such as having various religions, wars, suffering, but in time, we'll realize what God has in store for us. The only way of knowing what God has planned is to have faith. That doesn't mean that everyone has to follow or believe in the same religion, but having faith can mean in believing in something one strongly believes in.