Jeremy notes that whenever we see the penal element, we immediately think "substitution". He makes a great observation there. What we should also note, is that due to the predominance of Penal Substitution in our teaching, whenever we see substitution, we assume that it is penal.
This has come up a couple of times in the comments and I'd like to address it more publically here. Maybe I didn't make myself clear in my original posts, so let me clarify now: I deny Penal Substitution, but I don't deny Substitution in all forms. I only deny that any biblical substitution is Penal.
So. When Jesus Ransoms us, I freely admit that there is an exchange going on--His life for us as slaves. But I deny that there is any punishment/judgement going on there. Similarly when Abraham was going to sacrifice Isaac. Yes there is substitution with the ram. Yes, this is a type of Christ. But there is no punishment going on here. Etc. These are the most obvious examples, now we'll move to three less obvious ones:
1) Scapegoat: Jeremy points out that I must abandon the scapegoat as there is no sense that the scapegoat is in union with the Israelites once it is in the wilderness. I agree. He says that it is substitution. OK. But I deny that it is Penal.
Even when I believed in Penal Substitution, I had problems with the scapegoat being used as support for PS. The sins of the nation get laid on the goat, and then the goat is not punished! How is that support for penal substitution? If the scapegoat were meant to be a symbol looking forward to PS, then they would have to kill the scapegoat (any punishment short of death would be inadequate punishment for sin). But they don't.
Given that the scapegoat isn't punished, as best as I can tell the purpose of the scapegoat is not so much to be a substitute penalty, but to be a concrete visual demonstration to the nation that there is no longer any sin in the nation. That notion works perfectly well with both Penal Substitution and Penal Union, so I don't think that the scapegoat either supports nor denies either model.
2) Passover: I must admit that this one strikes much closer to home. I do not have a perfectly adequate answer to this one, but I must point out that (and Cary acknowledges) that the plague of the death of the firstborn was not sent as punishment for the Israelites' sins. (What sin would that have been? Not allowing themselves to be freed from slavery to the Egyptians?) As such, the sacrifice was a substitution, but not a penal one.
3) OT sacrifices in general: I've made my argument in the comments that the sin sacrifices were actually meant to be seen as union with the sacrifice, but that it eventually became (mis)understood as substitutionary. Regarding other sacrifices, however, I must point out that they were not meant to be penal, so even if you can show that they were meant to be substitutions, they don't support penal substitution anyway.
So. How do we define substitution?
rebecca's comments in this thread (#8 in the thread) sound to me to be almost exactly what I believe. However, she keeps calling it "substitution" while I lump most of what she says under the category of "union". Clearly we have some definitions crossed, so lets try to sort it out.
[First of all, as much as I respect the late Colin Gunton, his statement that the cross was "substitutional in that Christ does for us what we cannot do for ourselves" is a really bad definition. (Not that anyone here brought that up, but my advisor keeps quoting that as if it were a scriptural definition.) While Christ certainly does for us what we cannot do for ourselves, that isn't necessarily substitution. Gunton's "definition" certainly overlaps with the definition of substitution, and substitution may even be a subset of his definition, but the "definition" is far too broad to fit "substitution". It is probably a better definition of "service" or something like that. If Gunton's definition was correct, then a mother giving birth to a child would somehow be substitutionary as the child cannot give birth to herself. Or a surgeon doing bypass surgury is somehow substitutional as the patient can't do the surgery himself. But nobody would ever call these substitutions. (Sorry. Rant over.)]
Rebecca seems to think that if something is indirect, then inasmuch as it is indirect it is substitution. Meanwhile, I think that indirect participation is still participation, and thus union. (Rebecca agrees with this, I think.) But I don't think that the indirectness means that it is substitution. (I think this is where we disagree.) I think that this leaves us sharing tons of common ground, but we call that common ground different things.
So how can we tell if this is really substitution or union? I think that Adrian in his piercing comment in this thread cuts to the heart of the matter. He states: "I cannot accept...any sense in which we share in Christs punishment...We get let off the hook and are not punished". Adrian is staking out the ground clearly. Any participation in the punishment is outside the realm of Penal Substitution. He understands that if there is participation, even indirectly, then it has ceased being "instead of" and has turned into "together with".
So here is the real test to see if you agree with me. We'll drop the terms which we've become attached to and boil it down to the really essential questions: Do you think that we are indirectly punished in Christ? Or are we let off the hook?