2 Corinthians 5:21

‘Him who knew no sin he made sin on our behalf; that we might become the righteousness of God in him.'

And finally he gives the full basis of that reconciliation. It is because the perfect One, the sinless One Who knew no sin (1 Peter 2:22; Hebrews 4:15), was ‘made sin' for us. Our sin was in some way absorbed by Him. Just as in the Old Testament the offeror laid his hand on the sacrifice indicating that his sin now lay on the sacrifice, so was our sin laid on the greater Sacrifice, to be borne by us no more. There lies behind this the idea of the sacrificial suffering of the Servant in Isaiah 53:10, and indeed in the remainder of Isaiah 53. Being made sin He bore the consequences of sin. He suffered for sin, the just for the unjust, that He might bring us to God (1 Peter 3:18). And the result is that we become the righteousness of God in Him. Rather than being full of our sin, which has been laid on Christ, we become full of God's righteousness (either His righteousness or the righteousness which He has provided in Christ), which enclothes us and possesses us (Romans 5:19). Just as Christ absorbed our sin, so do we absorb His righteousness. Now we can approach God without fear of rejection, because we approach Him radiant in the righteousness of Christ. Thus are we fully reconciled to God.

‘Him who knew no sin.' The verb means to ‘know in experience'. In the Garden the tree was the tree ‘of knowing in experience good and evil.' In the first man, the earthly man, all partook of that tree, and became sinful (Romans 5:12). And in a sense all men continually taste of that tree for all being aware of good continually choose to experience evil, proving that they are sinful. But Jesus, the second man (1 Corinthians 15:47), the man from Heaven, knew no sin. It was something outside His experience. He knew only good. That was why He could be the unblemished sacrifice (1 Peter 1:19). The introduction of this idea here stresses the source of the righteousness of God which can be imputed to us. It was the Righteous One.

‘The righteousness of God.' God is the standard of all righteousness, and therefore the righteousness of God is righteousness in all its perfection, it is perfect righteousness. And it is that righteousness that is required for reconciliation. And in Christ it is not only accounted to us but implanted within us by His Spirit, the one to ensure our acceptance with God, the other to write it in our hearts that it might be revealed in our lives (2 Corinthians 3:3). For the similar idea of righteousness imputed and imparted to us in Christ see 1 Corinthians 1:30 where ‘He is made to us -- righteousness'. See also Philippians 3:9.