Why did Jesus have to die? Because at that moment, bearing your sin and mine, he deserved to die. Was the Father unjust by slaying an innocent man? No. Jesus had to die because on the cross He became the vilest sinner on earth. “He who knew no sin became sin for us, so that in him we might become the righteousness of God (2 Cor. 5:21).”
(This is another quote from the same blog I mentioned in my previous post, and the same post, "Lent for Dummies".)
The Orthodox understand this verse as metaphorical. Now metaphorical does not mean unreal! It means one reality is expressed as if it were another; or as Merriam-Webster says, “a figure of speech in which a word or phrase literally denoting one kind of object or idea is used in place of another to suggest a likeness or analogy between them (as in drowning in money).” A person “drowning in money” isn’t literally drowning; isn’t necessarily even in the water. But the reality expressed by the metaphor is that the person has so much money that if it were water instead of money, the water would be enough for a person to drown in.
Similarly, with 2 Cor. 5:21. In Jesus, “who knew no sin”, God makes sin concretely visible to us in its full ugliness and horror: the Son of God is crucified. The Crucifixion is the ultimate icon of sin: in the most horrific crime in history, God incarnate is judged and not merely put to death, but executed as if He had been a criminal, although He was innocent and perfect and all-holy and never deserved to die.
This death is portrayed everywhere in the New Testament as illegal and immoral: “Him, being delivered by the determinate counsel and foreknowledge of God, ye have taken, and by wicked hands have crucified and slain,” St. Peter tells the crowds on Pentecost. There was nothing just about it; in fact, Jesus’ death is the supreme injustice.
Still less would there be anything just about it if we were to take this verse literally, supposing a person could literally morph into a thing, and an abstract thing, at that: not “a sinner” but “sin”. Besides being impossible, it is a truly scandalous thought to suppose Christ could ever turn into a sinner literally, which is not what the verse says, much less the vilest sinner on earth, still less into sin itself, literally. But even if this were possible (and not blasphemous), then for God to blame the only innocent One for every sin that had ever been committed in the whole world would be the very opposite of anything that could be considered justice or legality or morality.
Notice, too, what St. Peter tells us God did: delivered Jesus into the hands of the wicked, by His pre-determined counsel. He does not say God the Father killed Him. God the Father did not. He is not the culprit.
(But if He were, then, since the Holy Trinity always works as with one will, one purpose, one mind, one power, we would have to say God the Holy Spirit also did it and God the Son also killed Himself to appease His own wrath. Else we would be pitting at least One of the Holy Trinity against at least One Other, in a manner not permitted by basic Trinitarian theology.)
In fact, Christ our God laid down His own life. That is, it was not being crucified that killed Him, not the bleeding nor the suffocation nor anything else man could do. Instead, He died by His own free will, at the moment of His choosing, with all His strength intact, as shown by the fact that the moment before His death, He cried out with a very loud, strong voice. Jesus had earlier taught: "I lay down My life that I may take it again. No one takes it from Me, but I lay it down of Myself. I have power to lay it down, and I have power to take it again. This command I have received from My Father." (John 10:17-18)
Death is the legal penalty for sin, and Jesus died, suffering that penalty just as if He had sinned, although, because He had not, death for Him did not literally mean He was being punished. Instead, He took upon Himself the same death which for anyone else would be punishment, but for a different purpose: in order to annihilate death by His encounter with it, just as a bright light in a dark room scatters the darkness by its very presence. That is how he “became sin for us.”