2 Corinthians 5:21 (ESV) … “For our sake he made him to be sin who knew no sin, so that in him we might become the righteousness of God.”
Paul affirms that Christ did not sin, though He was tempted (Matt 4:1–11; Mark 1:12–13; Luke 4:1–13; Heb 4:15).
to be sin This describes how God regarded Christ as sin for the sake of undeserving sinners (compare Gal 3:13). More specifically, Paul may be presenting Christ as a substitute for sinful humanity or he could be referring to Christ’s identification with sin through His union with sinful humanity. Another possibility is that Paul is interpreting Christ’s sacrifice in light of ot sacrificial concepts (e.g., Lev 4:24; 5:12; Isa 53:10).
the righteousness of God Through Christ’s death and resurrection, God demonstrated His righteousness by judging sin yet showing mercy to sinners. Here Paul refers to the idea of Christians becoming the righteousness of God. He may mean that believers, as a result of God’s justification, receive a right standing before God while Christ takes on their sins (Rom 5:8).
Finally, Paul could also be describing God’s righteous character, which believers receive and should live out in their lives. See Rom 1:17.