Why was God so harsh on people in the Old Testament and more forgiving in the New Testament?
My first reaction to that question is to say, "He wasn't," or "He is." He wasn't as harsh as you think, and he is more harsh than you think. But that may not be the most helpful thing to say.
It may be that we should just acknowledge that this question is probably coming out of reading lots of stories of battles—horrible battles—and lots of stories of harshness. There is a lot of death and killing and the earth swallowing up families in the Old Testament; and you don't read much of that in the New Testament, except for in Revelation.
So you read about Jesus having an incredible open-heartedness towards tax collectors and sinners.
So, yes, OK, it's there. There is something to this question. And the answer is probably signaled in Luke 4, where Jesus comes into the synagogue and he says, "This is being fulfilled in your hearing." He read Isaiah, and the day of the Lord is at hand. And what he reads, he reads and he stops at a certain point in Isaiah, just before he gets to the day of judgment and of wrath.
So with Jesus has come into the world salvation. "I did not come to judge the world but to save the world" (John 3:17). So the window that we have of Jesus in the world is a day of salvation, a day of offering forgiveness, a day of dying for sinners, and a day of holding out his hands and beckoning.
And all that in the Old Testament was preparation to show how wrathful and how just and how true and how glorious God is, and how terrible sin is. And now you're getting Jesus, who is mercy incarnate, grace incarnate, forgiveness incarnate, open-heartedness incarnate, saying, "This is what is available for you."
So I think there is an intention that the Old Testament look bleak, sin look horrible, God look just, and that there be much less mercy, proportionate to what you see in the three years of the ministry of Jesus. And that's intentional. This is what God's heart is to the world right now. Come!
And then the New Testament closes with another Old Testament. The Book of Revelation is horrific! So we're in a window right now.
So if people are watching this right now, they should feel, "I'm in a window of mercy, and I should embrace it so that I can escape the wrath when it comes again."