The penal substitution theory consists of two claims:
- Christ's sufferings are a substitute for our justly deserved punishment.
- Christ's sufferings are a punishment of Christ.
The gravest objection—the inappropriateness of Christ's being punished—to the penal substitution theory is an objection not to (1) but to (2). At the same time, the Biblical evidence for the penal substitution theory is largely evidence only for (1), not for (2). Consequently, it seems like one would do well to simply adopt (1), while rejecting (2). The resulting theory would be a theory of Christ's substitutionary sacrifice, but it would be penal only on our side, not on Christ's side. (This idea is inspired by a paper Adam Pelser gave at the SCP meeting in Niagara last year; Pelser was advocating a particular theory that entailed (1) without committing him to (2).)
I am not claiming that holding on to (1) while rejecting (2) solves all the problems of the atonement. The major difficulty of just how (1) manages to be true—just how Christ's sufferings manage to substitute for our punishment—remains.
I think (1) is plausible in some cases. Suppose I raped Captain Smith and tortured him to within inches of his life while I was working for a terrorist organization that captured Captain Smith. Later, Captain Smith jumped on a grenade to save my life, yelling that he forgave me what I did to him. Even if the death penalty were appropriate for my rape and torture of Captain Smith (I think rape and torture deserve the death penalty, though I also think we have a duty of mercy which prohibits us from employing the death penalty unless it is necessary for the protection of society), if I've accepted Captain Smith's forgiveness (and thus repented—it's not a real acceptance of forgiveness otherwise, I think), I think there would be something inappropriate about executing me for what I did to Captain Smith—there is a way in which his suffering death on my behalf substitutes for the punishment owing me. (This does not solve all of the problems with the atonement. One of the difficulties is with the way Christ's sufferings atones for sins we committed not just against God—there, I think we need to say something about how all sins are primarily against God. But it is enough to show that (1) is not in and of itself absurd.)