Source: Jacob Neusner's Introduction to Rabbinic Literature, 257.
"The Lord is a man of war, but the Lord is in no way comparable to a man of war, making war in a supernatural way, specifically by retaining, even while making war, the attributes of mercy and humanity."
Judaism believes that God has justice and mercy, each of which tempers the other. This doesn't really coincide with certain evangelical presentations I've heard, which treat God as if he has a split personality, or which act as if God's justice was totally appeased through Jesus' death on the cross. Judaism seems to view God as an organic whole: when he punishes, he uses mercy.
I'm not sure if that always works. God wasn't all that merciful to wicked Er when he killed him, after all (Genesis 38)! But the rabbis sought to make God look humane, even through his just wrath. When God drowned the Egyptians in the Red Sea, he chastised the angels who were rejoicing, saying that the Egyptians are his children, too. And the rabbis contend that God offered the Canaanites an opportunity to repent and surrender before he had the Israelites destroy them.
The rabbis still do not resolve a problem I have, at least not completely: how do I know if I'm on God's good side, or on his bad side? After all, there are good things that I do, but also bad things. I suppose my conclusion is that God continues to reach out to me, even when I'm not good. That's what families are supposed to do, right? Why wouldn't God act this way?
Also, if God tempers his justice with mercy, what's that do to the concept of eternal hell? I know there are strands of Judaism that embrace it, but are they like George MacDonald, in the sense that they believe God has compassion for the tormented souls?