The acid test for atonement theology is to account for the necessity and the efficacy of the death of Jesus as the culmination of the through line of God's covenantal action. Let us address these two concers in order. First, the necessity of the cross. If the cross saves merely by manifesting some universal truth--"God is on the side of the victims"; "God forgives us no matter what"--then it does not really change anything, except for our ignorance of the principle. This position suffers from two weaknesses. First, it leads to the eclipse of Jesus; for once we grasp the principle, the particular story and the events it relates are dispensable. Second, the preaching of the cross becomes a reassuring affirmation ("God's OK; you're OK"), not a radical transformation.Vanhoozer doesn't quite say it in this way, but here's how I'd phrase what I think he's trying to say: We can't answer why Christ died; we can only answer what Christ's death accomplished. In general, he's saying that the drama of God's action in the world transcends all principles, whereas other approaches make principles transcend the drama. When principles transcend the drama, you get statements like, "Jesus died so that we could be saved from our sins." When the drama transcends principles, you get statements like, "Jesus died; therefore your sins are forgiven."
The difference sounds subtle, but it's really quite profound. It means God doesn't act according to fixed principles; rather, principles are derived from God's actions. Vanhoozer doesn't explore the uncomfortable nature of this claim. It means God really is fundamentally inexplicable. We don't actually know why the theodrama has played out this particular way, because there is no why that exists prior to God's actions themselves (at least as they exist collectively as a single drama). Hence God's response to Job. Hence the "foolishness" of the gospel.
It's a shame I had to read for so long to get to this. It really is an idea worth interacting with.