ddgently said:
The logical problem with this goes to the question why? Why must sin be punished? Is God bound by a system of justice that is greater than he is?
Justice is an attribute of God. It's not that he is bound to a system greater than himself; rather, it is he who established what justice is, flowing out of his own good character, and in effect he holds himself to his own standards. Additionally, God is perfectly just: he applies his standards fairly and equitably to all creation.
Sin must be punished, because if sin is not punished, then God is not just. And sin must be punished equitably: if God forgives some sinners but not others, merely because it is his prerogative to do so, then he is again not demonstrating justice, but capriciousness. We wind up with a god like the Muslim Allah, who ostensibly judges all men by weighing their good and bad deeds in the scales, but ultimately decides their fates on his own whim and so there can be no promise of paradise even for the most faithful Muslim.
The problem with the atonement is not the nature of forgiveness. It is with the nature of justice. God's forgiveness is based objectively in the satisfaction of his justice. There is no mercy unless justice is properly understood.
Not to mention the fact that normally PNA doesn't work. Can I volunteer to go to jail for the bank robber, or the drug dealer who was sentenced in court yesterday?
Just because no system of jurisprudence incorporates some form of penal substitution, doesn't mean that a) such a system could not theoretically exist; or b) that divine justice therefore cannot incorporate it.
First, it is God himself who established the system of penal substitution, through the system of Temple sacrifices. They were incapable of truly or permanently taking away sin (Heb. 10:11). But they did tell the people both that sin required the taking of a life, and that forgiveness was available. The Temple system of course ultimately pointed to the sacrifice and intercession of Christ, who was able to propitiate the Father and offer forgiveness once and for all. As a matter of fact, the weaker theories of the Atonement (such as Abelard's moral influence or the Socinians' example of obedience theories) can't make any connection between Christ and the Old Testament saints. Only penal substitution theory can explain their salvation.
But of course, sin doesn't have to be punished. We're told in Scripture that in addition to sinning against God, we sin against each other. And we're commanded to forgive freely.
So if I my friend lies to me, I don't get to punish him for it before I offer forgiveness. I certainly don't get to punish some innocent third party before I offer forgiveness. Rather, I'm called to forgive freely.
But that forgiveness isn't exercised merely on our own prerogative, is it? Eph. 4:32 says, "forgiving one another,
as God in Christ forgave you." We forgive because we have been forgiven. And we have been forgiven
in Christ, because Christ died for us: "[M]y blood of the covenant . . . is poured out for many for the forgiveness of sins" (Matt. 26:28). So the forgiveness we show others is predicated on an objective basis, just like the forgiveness God shows us.