Here's the boring historical part. If you're with me so far, you don't necessarily have to read it. But if you're confused, keep going.
Many of my correspondents don't know this history and insist instead that the Blood Atonement theory is the earliest. It just isn't so. They believe this because they find evidence for it in the Scriptures, but as I've said, this is a matter of your favorite Scriptures lighting up for you, in accord with how you've been taught.
The appearance in history of the Blood Atonement, or Substitutionary, theory can actually be located pretty precisely, in the work "Cur Deus Homo?" ("Why Did God Become Man?") by Anselm, Bishop of Canterbury, in the 11th century. Anselm's idea is foreshadowed in some earlier writers, like Tertullian, but it was not the general view.
The general view of the early church was not as crisp, as thorough, as Anselm's. And this is why Catholic and Protestant theologians have seen Anselm's theory as a great advance. Henry Bettenson, in his anthology "Documents of the Christian Church," calls "Cur Deus Homo," "one of the few books that can truly be called epoch-making."
Catholic and Protestants have never claimed that Anselm's Blood-Atonement theory is the earliest; they've said it is the best. It was a breakthrough. That implies something else came before.
Anselm's theory, as we know, is that our sins create an overwhelming offense against God's honor, a debt. God cannot merely excuse this offense and wipe the debt away, because it constitutes an objective wrong in the universe; justice would be knocked out of balance. There must be punishment.
Anselm: "Let us consider whether God could properly remit sin by mercy alone without satisfaction. So to remit sin would be simply to abstain from punishing it. And since the only possible way of correcting sin, for which no satisfaction has been made, is to punish it, not to punish it is to remit it uncorrected. But God cannot properly leave anything uncorrected in his kingdom. Moreover, to remit sin unpunished would be treating the sinful and sinless alike, which would be incongruous to God's nature. And incongruity is injustice. It is necessary, therefore, that either the honor taken away should be repaid, or punishment should be inflicted."
He goes on to say that "no sinner can make" complete satisfaction for sin. "None can make this satisfaction except God. And none ought to make it except man...One must make it who is both God and man."
Because Christ did not deserve to suffer for us, but paid the debt voluntarily, he "ought not to be without reward...If the Son chose to make over the claim he had on God to man, could the Father justly forbid him doing so, or refuse to man what the Son willed to give him?"
I think most of you will recognize this. It is the standard view of traditional Catholics and Protestants.
During the Enlightenment theologians began to criticize this theory as legalistic, as too rooted in the Old Testament and not enough in the New, as portraying a God who hardly seems to be one of love. They began to develop an alternative theory which was little concerned with punishment of sin; instead, Christ's sacrifice was meant to move and inspire, so that we voluntarily return to God, and God is moved to reconcile with us. This theory is called "exemplary" because Jesus is the example rather than the sacrifice. It's proponents claimed to root their view in Abelard, a younger critic of Anselm. The big debate in the 19th century cast these two views as "objective" and "subjective."
Because of this, conservative Christians in the West are disposed to see any attack on the Substitutionary theory as a move toward liberalism.
That is not so. There is a whole third viewpoint, which prevailed throughout the first millennium, and continues outside Western Christianity today.
***
Now I'm going to describe this theory. Though I've described it from time to time in my writing, I have a hunch that no non-Orthodox could explain it back to me, because its simply too unfamiliar. It's strange to us; its premodern. It has the Devil in it. A theory so odd doesn't fit any of our categories, so as soon as we read about it we forget it.
I've heard that you have to be exposed to an unfamiliar idea seven times before you remember it. So read this section seven times.
Without grasping this alternative classic theory, we fall back into presuming that, if it ain't substitutionary, it's modern, liberal, and bad.
This theory, in short, does not consider the possibility that God could not just forgive us. It presumes that he *does* just forgive us. The thing that so troubled Anselm--the image of a great offense against God that could not be paid or remitted--didn't occur to the early church.
However, "the wages of sin is Death." Because we are sinners, we are captives of Death. The term means more than mortality: it is a package including the Devil, evil spirits, temptation to sin, and so forth, "the Tyrant." We have sinful hearts that incline to choose self, and this cooperation with Evil keeps us infected with the seeds of our own destruction. We are responsible for our own fate, because we cooperate with Evil. We are powerless to escape this fate.
Note that the emphasis is not on sins being an offense against God. It is more organic, like a disease inside a person. But imagine that the person loves and caresses the disease, and joins his will to it in affirmation. What can be done? What would a loving parent do?
The classic view sees God the Father and Christ his Son agreeing to rescue lost humanity. The Son must actually go into the realm of Death and break it open. He sets the captives free.
The Cross is a high point in this story. But it is part of a complete story that begins with Christ's decision to become human, as we see in the Phillippians 2 hymn. It proceeds through the Resurrection and is crowned by the Ascension and "sitting at the right hand" and even the final Judgement. The whole story is what saves us. (by the way, salvation is organic too, and transforms the entire person; its not merely the legal remission of sin. It's called theosis.)
When I was researching this a few years ago I asked some Patristic scholars what I should read to get a handle on the early church theory of the Atonement. They replied that there really isn't one, in terms of Western thinking. The best thing to read would be "On the Incarnation," written by young Athanasius about 318. I kept saying, No, I'm not asking about the Incarnation, I'm asking about the Atonement. They said, It's the same thing. Salvation is the whole story. (You can probably find "On the Incarnation" on line; its not very long. I like the edition published by St Vladimir's Seminary Press, which has a great introduction by C S Lewis.)
Here's an example of how little the early church dwelt on the pain of the Passion. Athanasius asks rhetorically, If the whole point of the rescue was to get Jesus into Hades, why did he have to be crucified? Why couldn't he just have died peacefully as an old man? (You might be wondering that yourself about now.)
Athanasius reels off a lot of reasons in reply: that the Author of Life could not have possibly gotten sick, that the Crucifixion was a public death and so Christians wouldn't be accused of faking it. But he never says that it was necessary for Jesus to suffer in order to pay our debt.
It was necessary for him to suffer in order to get into Hades, yes. It was the price of admission. But not a punishment. Christ achieved our deliverance at the cost of his blood, but it was not a payment.
As I said, the early church writers did not try to work out a theory as crisp and complete as Anselm's. They agreed on the central reality--Christ went into Hades and set us free--but did not establish any detailed explanation of how it took place. The language in Scripture about "ransom" and "sacrifice" was explored poetically, without an attempt to establish explicit doctrine. Gregory Nazianzus says that such language is always bound to lead to uncertainty. If a "ransom" is paid to a kidnapper, it wasn't paid to God; God wasn't holding us hostage. But if it was paid to the Devil, the very idea is outrageous. The Devil was a usurper and had no right to fair payment. It couldn't be a sacrifice in payment to the Father, because the Father would not even accept the sacrifice of Isaac--how much more appalling would be the sacrifice of his own Son. So, Gregory concludes, we just can't press these images too hard.
It definitely cost Jesus his life's blood to rescue us. It was a ransom in that sense. He offered it in obedience to the Father. It was a sacrifice in that sense. When the sacrifice to the Father was explored in more depth and likened to Temple sacrifice, as in Hebrews, it was treated poetically, typologically, not literally.
It was this softness of logic that makes the classic theory frustrating to Western Christians, and elicits impatience. The answer "It's a mystery" sounds like "it's unreliable". Here we must note another influence on our thinking: the Scholastic movement and Thomas Aquinas. In the West we developed a tradition of vigorous intellectual inquiry, and to some extent divided this from popular piety, so that theology became a realm for experts. (An aside: this worship-study split shades into a heart-mind split, and I speculate is one reason Western worship services, heavy on emotion, are attended by more women than men. It's not that men are intrinsically less religious--look at Islam and Orthodox Judaism.)
It's hard for us to imagine a Christians culture in which people didn't pursue a theological question to the very end. The compensation is that study and worship are united, so that what we understand moves us to love God, and love moves us to deeper understanding. It would be strange to even to think of those as two different functions, because we are a unity. There are things we don't particularly need to know in order to live on this earth and follow our Lord. Early Christians would say that the exact mechanism of the Atonement is one of those things. We know that Christ has rescued us from the Evil One, and that we must exercise constant vigilance to keep from hurling ourselves voluntarily back into the pit. That's all we need to know.
To answer the initial question of "When did treatment of Jesus' suffering change?" it appears that graphic meditation on the Passion begins about the 14th century. In medieval times, too, the depiction of the Devil is reduced in significance, and he becomes a semi-comic figure. In the substitutionary atonement there is really no role for the Devil; the whole transaction is between Christ and the Father, so the Devil fades away (not in reality, of course).
I've been Orthodox ten years and only recently begun to see how different these views of the Atonement are. Every step of the way as these paths diverge they lead to divergent views of everything else: what sin is, what forgiveness is, what the Father's love is like, even the problem of evil (in the Christian east the West's big question, "how can a good God permit evil?" doesn't occur; we know evil is in the world because our sins keep polluting it, keep opening the door. Our sins empower the Evil One, and he delights in hurting the innocent, not only because he enjoys their suffering, but relishes the grief of observers as well.)
An unfamiliar idea like this is disruptive and unsettling, and prompts floods of other questions. I may not have time to answer them all. But I hoped, by this message, to at least lay out the groundwork.