Why is God so wrathful in the Old Testament and so compassionate in the New Testament?
I actually don’t think that is true. You have to understand that in order for God to get the human race to the point where they could understand New Testament teaching, it took a long time of potty training, nurturing and growing up. That is why the Bible is called progressive revelation. As time has gone by, more and more is known because people didn’t know it earlier. If you look at Jesus’ statements in the New Testament, they are every bit as stern as the God of the Old Testament. In fact Jesus had more to say about Hell than any other subject. I think that makes them pretty much the same.