Surprise surprise. I have had nothing to say about atonement theory and have not debated the matter to any purpose. I have not debated subordinationism either (they are related), where some trinitarians think it essential that the Trinity and not Arian heresy asserts equality - funny then that the heteretical denomination in Britain, the Unitarians, along with Quakers, has consistently been the most equalitarian. The stress on unity for longer has had a longer impact, I suggest, whether this is divine unity or human unity.
I don't care how Steve Chalke changes his mind (I do care that he's involved in British school education). I read a blog entry like Rachel's, done in the form of an academic essay, arguing about penal substitution as atonement theory, and it fails to address never mind answer the simple question: just how does all this work?
I live in a world view that demonstrates evolution. Evolution is what by accident turned big reptiles into birds and gave space for mammals to become humans; evolution is always and everywhere local and specific. It's based on comparative advantage and death in the particular. I also have a world view that explains scientific causality in general, and it's very complex, with technical materials now ever more incredible as a direct result of understanding the very small and the transformative. I understand mass research in figures and deep research in words (meanings). The world is mathematical, it is also chaotic in generation but systemic in relation (as is evolution). History is important, and has many schools of historiography, but identify primary sources as necessary and special whatever the craft of the story telling, just as the craft of writing is necessary to summarise a thick research of the anthropologist.
And thus I have not a clue how atonement works. I do know about exchange and gift theory, but that works around ritual between people as we have them and binds them together stronger as a group. Exchange theory is part of economics, part of social contract, sex, art, part of religion. A relatively worthless token can be exchanged where material loss brings spiritual benefit, where the binding together comes. So a eucharistic ritual is like that, and the Roman Catholics strengthen it by claiming real presence, and by its ahistorical ritualistic participation in the crucifixion of the deity. If you believe its ridiculous pseudo-science, or you can have a faith-view that requires ever more mental effort, it necvertheless still requires a ritual to happen and to bind the group giving it identity and purpose - in this case, Christians.
But the gift-exchange of Christ for sin is nothing but mental effort. There is no objective basis for it at all, no method by which there is any transmission.
We need to be historical to look for what happened, and need to be scientific for mechanisms that do actual work. The history is that the Romans extended their empire around the Mediterranean. The edge of empire was a cruel place and irritants received short shrift. One of the end-time preachers (and healers) went to Jerusalem to preach the end of the world as we know it and preparation for a new reality, using the biblical sources like the suffering servant, nudging his God by self-importance to bring in the expected end, and was (like many) put to cruel death. A small group expected him to return from heaven as the actual messiah, a process of escalation of titles that didn't stop, and this group was fortunate to have an associate of talent from outside who created a salvation faith of Gentile appeal through what the Jews had as a messiah. First he favoured law, then he favoured messiah. But all these ideas are culturally relative and no longer explain how the world works. Jesus was wrong, they were wrong, but they thought as they did at the time. For a historian, the biblical sources are all secondary: they are primary only in regard to the beliefs of early Churches or communities. My history is reconstructive, it's all that is available, and is open to challenge but not more certainty.
What we have now are ethics, and we think Jesus was a good ethical type of person, but it is historically impossible to say he was supremely ethical simply because we don't have the information about him or others. As for him being sinless, it's only theological because as a human being he presumably had to grow up and learn. And any human is as fully human as any other. The notion of atonement is that either a God has to die or a purely sinless full human (or both - indeed the sinless human is as God). But it is simply a belief, a mental act, and one without historical back-up. Nor is there any applicable history or science to him being as the opening of the resurrection (the first) where bodies rise up. Death involves rapid brain damage, and there is no continuation of consciousness, and resurrection that follows death ought to be subject to the 'energise' test in Star Trek where all who energise must utterly perish, the people who then reconstruct are but carbon copies with memories. If you perish, the rest is copying.
Some might accuse me here of literalism or stupidity, but I am accusing the Christian of overt objectivity and more than can be claimed. There is no such thing as atonement, except as a kind of subjective mental act, a kind of delusion.
Furthermore, the notion that we are saved and changed, or the world is being restored, might have truth in it in places but is far more likely that people are more rational, more sympathetic, because of course at the same time we remain having hideous conflicts and wars and tribalisms. The saddest sight of recent times is the Buddhist monks of Burma showing nationalist and violent tendencies and wishing to ban marriages of Buddhist women to Muslim men. The viciousness of the war in Syria goes without saying.
Christian theology, like whether it is substitution or penal substitution just talks to itself. Recently I read some material about the younger James Martineau and others in Liverpool and the introduction of the Unitarian domestic mission there for people who hadn't the clothes to wear to go to church. The cultural assumptions about the necessity to hear Christianity show that they lived in a completely different worldview to our own, even from the 1830s onward. Martineau was later to revise his ideas, though he never enacted the implications of them away from Christianity as he retained a more conservative liturgical output. But it's as if the whole explanation of reality has simply collapsed: Christianity is now a mythology and nothing different from any other mythology. Argue this way or that way, but it does not connect with the ways we explain things today, ways that produce results and repeat the results.
Religion has now to be different: to be reflective, to be an overview, a pause, yes with rituals to bind, but not an alternative universe unless, of course, one fancies fantasy.
Simon Schama presents The Story of the Jews - not, we note, an ongoing history of the restoration of the world in transit. It is a story of ethnic identity with rituals. The Reformed in England even wear top hats during their ritual. He points out that there is no evidence for Moses (and none for Abraham, of course) and that the biblical writing was more recent. Archaeologists find the Bible a distraction, he points out. Quite, because archaeology has its method too, and one that has causal impact. Time Team on Channel 4 used to explain things and made corrections. And that's the difference. Story is important to shaping lives, and the Christian story can shape Christian lives, but please don't be self-fooled by arguments that have no anchorage in anything other than story.