The parable is very colorful but perhaps does not exactly describe the evil of penal substitution. As I have usually heard it, penal substitution does not say that God would so hate sin that he could not help but execute punishment out of his immense, untamable anger.

What the theory does say, however, is not any better: God would be happy to just forgive sin but, unfortunately, law requires punishment! If he cancelled the punishment, by this cancellation he would also destroy the executive power of the law, and because the whole Universe is constituted around the law, he would also throw the entire Universe into anarchy and chaos.

Thus, there are laws by which everyone in God’s Universe must live, and keeping of these laws are secured by a system of punishemt and reward. If you obey, you have a reward of eternal life, and if you disobey, you are punsihed by eternal death.

Because all humanity has transgressed the law(s), it needs to be saved. The process is described as follows:

Problem: Humanity has transgressed the law. The law requires punishment. If God executed the punishment, we would just die without any hope.

Solution: God punishes his Son instead of us. Now punishment no longer awaits us, and we are given the reward of eternal life.

So — the problem is legal, and the solution is legal. No wonder Christianity is so apt to slip into legalism. If the cross of Christ is the central doctrine of Christianity, then its interpretation becomes a crucial issue.

Is the Bible about LAW, or is it about RELATIONSHIP? Is Christianity about LAW, or is it about RELATIONSHIP?

I see the main problem with penal substitution that it is a seat of legalism. Punishent and reward cannot be permanent principles in an eternal, ideal society.