As a minister of the Gospel, I have a question that I was recently asked and I was curious if you had ever been asked the same: How can we preach a loving God and Christianity to Muslims if our God in the Old Testament was a violent God just as their Allah? I understand how and why God needed to show His power by using the small nation of Israel to show His power; however, I know individual Muslims can give a rebuttal of that Allah is requiring them to do the same. I think it would help the brethern to have a collective answer to combat Islam.
First, we need to understand that the physical violence advocated by Islam is totally different from how the New Testament teaches Christians to treat their neighbors and their enemies. See: Understanding Islam.
But is the God of the New Testament different from the God of the Old Testament? The answer the Bible gives is "No." "Like a cloak You will fold them up, aand they will be changed. But You are the same, and Your years will not fail" (Hebrews 1:12). "Jesus Christ is the same yesterday, today, and forever" (Hebrews 13:8).
The Bible never advocates personal vengeance as Islam does. Yes, in the Old Testament God punished the wicked, but it was God who made the decision, not man, even when God used men and their nations as tools for the punishment. See: How can God command us not to murder when God murdered in the Old Testament? and Can God be fair if He doesn't give a sinner another chance? Also, when God saw the need to readicate sin, it was for a limited time and in a limited region. Islam basically declares war against any contrary belief.