The very early theologian St. Irenaeus built his interpretation of the Christian faith around the idea of recapitulation: who Adam was and what he did wrong is replaced and made right by Christ. Irenaeus derives the idea, of course, from Romans 5. The primal exchange in the whole human family should have been for the good—our forefather Adam setting a pattern of righteousness for all his descendents—but it turned out for the bad, and his death became our death. To interrupt that exchange, wherein each of us stands in the place of Adam and sins again, Christ steps in and takes Adam’s place as well as ours. And the free gift is not like the trespass!

This exchange for the sake of our salvation was already foreseen in Isaiah's writings on the suffering servant in ch. 53. "Surely he has borne our griefs and carried our sorrows... He was wounded for our transgressions; he was crushed for our iniquities; upon him was the chastisement that brought us peace, and with his stripes we are healed... The LORD has lain on him the iniquity of us all... Who considered that he was cut off out of the land of the living, stricken for the transgression of my people?" Here it is well worth remembering Luther's dictum that this suffering servant absolutely must be the eternal Son of God incarnate, or the exchange is hardly joyful, rather a wicked scapegoating. We can also imagine that Luther the Old Testament scholar had deeply internalized the close relationship between atonement and justification as suggested by some verses a little later in Isaiah 53: "By his knowledge shall the righteous one, my servant, make many to be accounted righteous, and he shall bear their iniquities... He bore the sin of many, and makes intercession for the transgressors."

For the evangelist John, the exchange is first located in the relationship between the Father and the Son, the latter standing in for the former in the chain of knowledge and love in the communication of God with the world. This can happen because “the Father is in me and I am in the Father” (John 10:38). That exchange gets extended to us through the gospel so that “you will know that I am in my Father, and you in me, and I in you” (John 14:20). This isn’t just pious talk or inspirational imagery. It is a real mutual indwelling. If that weren’t so, the remarkable commission at the end of John’s gospel would be impossible: “Receive the Holy Spirit. If you forgive the sins of anyone, they are forgiven; if you withhold forgiveness from anyone, it is withheld” (John 20:22-23). Everyone knows that only God can forgive sins. But through the gift of the Holy Spirit, mere humans can do what only God can do, the apostolic communicatio idiomatum. Because, to move back in the other direction, “whoever receives the one I send receives me, and whoever receives me receives the one who sent me” (John 13:20). John makes no confusions about the ultimate identity of anyone; God is God and humans are humans and that boundary is not blurred. But love and the gospel effects such an intimacy of identification that receiving the messenger is really the same as receiving the Father.

Though we normally attribute this kind of language to John, it also appears in the Synoptics. Matthew in fact sounds uncannily johannine when he presents Jesus’ words: “Whoever receives you receives me, and whoever receives me receives him who sent me” (Matthew 10:40). Luke builds on it in the negative sense, highlighting the peril of rejecting the messenger: “The one who hears you hears me, and the one who rejects you rejects me, and the one who rejects me rejects him who sent me” (Luke 10:16).