From a human point of view this emphasis on the cross [in the New Testament] is baffling. Every prudential consideration suggested that these first Christian preachers should divert attention from it as much as possible. To Jewish ears, the idea of a crucified Messiah was a contradiction in terms. To Gentiles, the claim that the salvation of the world had come through a crucified Jewish criminal was an absurdity. To both Jew and Gentile, the suggestion that death, particularly death on a cross, could bring eternal life, was blasphemous idiocy; had the early church had a professional director of communications, he would have said, categorically, "We don't do the cross! Stay on message, and focus on his wonderful ethical teaching."
It is the cross itself that requires a theodicy. How can God justify what he did at Calvary? What gave him the right to sacrifice his own Son? Only the doctrine of vicarious punishment can provide an answer. The sword falls at the precise point where justice located the sin of the world: in Jesus own body, on the tree. The sword falls here because it is right that it should fall here; and it is right because 'in my place condemned he stood.' Otherwise the cross is a black hole; an irrational evil, the act of a capricious or malevolent deity.