In the Hebrew Bible the definition of injustice is to acquit the guilty and condemn the innocent. At the cross the greatest injustice–acquittal of guilty humanity, condemnation of the innocent Son of God–is somehow taken to satisfy God’s justice. So the cross is paradoxical if looked at in simple legal terms. But sometimes paradox is the mark of deep spiritual truth.
The idea that mercy entails suffering for the one needing forgiveness is not absent from the Hebrew Scriptures. “Blessed be the LORD, who daily bears our burden. The God who is our salvation.” Ps 68:19.
Joseph suffered from the sins of his brothers, but by so doing became the agent of their salvation (Gen 45:5-7). Moses had to carry Israel in their grumbling and sin in order to bring them to the place of rest (Num 11:11, 14).
The object of God’s work is to restore intimacy between God and people. The “cost” of intimacy is vulnerability. Anyone who has been in a close relationship knows that. It’s not an arbitrary cost, it’s just in the nature of relationship. And the cost of vulnerable contact with evil is suffering. Again, it’s in the nature of sin. “Can a man take fire in his bosom and his clothes not be burned?” (Prov 6:27). To restore a broken relationship with us as sinful humans, God had to draw vulnerably close to us in Christ. And the cost of that approach was the natural consequence of evil.
I don’t pretend that this is a complete answer. Ultimately, the nature of God’s regenerative work through Jesus is too deep to be plumbed by the human mind.
But it is not a matter of God needing to be angry at someone–anyone–so that we could get away Scott free with all our selfishness. It’s much deeper and more profound than that.