Some Protestants argue for justification by faith alone by appealing to 2 Corinthians 5:21, which says, “For our sake he made him to be sin who knew no sin, so that in him we might become the righteousness of God.” Protestant pastor John MacArthur even calls this verse the “heart of the gospel” when it comes to belief in sola fide, or justification by faith alone.
On the face of it, this doesn’t sound like it has much to do with us needing only to make an act of faith in Jesus in order to be saved. But Protestant apologists like MacArthur will say our salvation comes not from anything we do, but from the simple recognition that Jesus has already done everything that is necessary to rid us from sin. Through an act of faith, God “swaps” our sins for Christ’s righteousness, and that is why we can spend eternity with him. Jesus doesn’t literally become a sinner, but he is literally punished for our sins because now he has them.
When the Father sees the Son on the cross, he sees our sins and pours out his wrath upon the Son. But when the swap happens and God looks at us, he doesn’t see our sins anymore; he just sees Christ’s righteousness. Think of it as a theological Freaky Friday.
What’s important to remember is that our own righteousness hasn’t changed. Instead, God has covered our sins with Christ’s righteousness. Martin Luther is believed to have compared this to how dung heaps in the countryside would be covered with pure white snow. The dung heap remains, but it is no longer seen.
But this is not how 2 Corinthians 5:21 was traditionally understood throughout Church history.
Several Church fathers said this verse was an allusion to coming in the likeness of sinful flesh, or just the Incarnation in general, and has nothing to do with imputation of sin. St. Augustine said, “Therefore having no sin of his own; nevertheless, on account of the likeness of sinful flesh in which he came, he was called sin, that he might be sacrificed to wash away sin.” Even John Calvin used this verse in this way. When he was defending the importance of Christ’s humanity in the atonement, he wrote the following:
Although Christ could neither purify our souls by his own blood, nor appease the Father by his sacrifice, nor acquit us from the charge of guilt, nor, in short, perform the office of priest, unless he had been very God, because no human ability was equal to such a burden, it is however certain, that he performed all these things in his human nature. . . . Righteousness was manifested to us in his flesh. . . . He places the fountain of righteousness entirely in the incarnation of Christ[:] “He has made him to be sin for us who knew no sin, that we might be made the righteousness of God in him.”
The point is not that Christ has become our sins, but that Christ has offered himself for humanity by taking on a human body. This corresponds to Romans 8:3, which says, “For God has done what the law, weakened by the flesh, could not do: sending his own Son in the likeness of sinful flesh and for sin, he condemned sin in the flesh.”
Another interpretation of 2 Corinthians 5:21 is that “made him to be sin” means “made him to be a sin offering.” The Greek word for sin in this passage can also mean “sin offering,” or what is sacrificed to take away sin. Another place where we find it is Hebrews 10:6, which quotes Psalm 40, which refers to sacrifices. It literally says in Greek: “Burnt offering and for sin you have not delighted in,” so most translators render “sin” in this passage “sin offering” because that makes the most sense of the context.
It’s reasonable to conclude that the same is true of 2 Corinthians 5:21 because Paul makes it clear Christ himself is a paschal sacrifice. He says in 1 Corinthians 5:7, “Cleanse out the old leaven that you may be a new lump, as you really are unleavened. For Christ, our paschal lamb, has been sacrificed.”
So, to summarize, 2 Corinthians 5:21 does not refute the Catholic understanding of Christ’s atoning death. Moreover, it’s perfectly compatible with the Catholic view of Christ offering himself as a sacrifice that pays the debt incurred by all the sins ever committed. It is then up to each individual to freely choose to allow God to apply the effects of that sacrifice to his soul. This includes being baptized and being initially saved, and then living a life of obedience to God and not throwing away the value of Christ’s sacrifice. That’s why Hebrews 10:26-27 says, “For if we sin deliberately after receiving the knowledge of the truth, there no longer remains a sacrifice for sins, but a fearful prospect of judgment.”
We should take heart that Christ doesn’t just legally expunge our sinful deeds from a ledger, but transforms us as we receive his righteousness. 2 Corinthians 5:17 even says, “Therefore, if any one is in Christ, he is a new creation; the old has passed away, behold, the new has come.”