Penal Substitution and Union with Christ

Steve Jeffrey, Michael Ovey, and Andrew Sach write:

"Union with Christ explains how the innocent could be justly punished - he is judged for others' sins, which, by virtue of their union with him, become his. Conversely, it explains also how the guilty can be justly acquitted - believers are one with the innocent Lord Jesus Christ, and so his life of perfect righteousness is rightly imputed to us. The apostle Paul captures both sides of the exchange in a single verse: 'God made him who had no sin to be sin for us so that in him we might become the righteousness of God' (II Cor 5:21; italics added)."