Passage
Him who knew no sin he made [to be] sin on our behalf; that we might become the righteousness of God in him.
2 Corinthians 5:21 (ASV)
Nearby Context
2 Corinthians 5:19 to wit, that God was in Christ reconciling the world unto himself, not reckoning unto them their trespasses, and having committed unto us the word of reconciliation.
2 Corinthians 5:20 We are ambassadors therefore on behalf of Christ, as though God were entreating by us: we beseech [you] on behalf of Christ, be ye reconciled to God.
2 Corinthians 5:21 Him who knew no sin he made [to be] sin on our behalf; that we might become the righteousness of God in him.
Study Lenses
The verse centers on "knew", "behalf", "might", "become", and "righteousness". It is saying that the verse draws attention to "knew" and "behalf", so its meaning should be read from those terms before moving to application.
The prior verse says "We are ambassadors therefore on behalf of...", giving immediate footing for "knew" and "behalf". In 2 Corinthians context, the local focus is Christ, faith, and discipleship.
A plain takeaway is to answer the verse's own emphasis on "knew" and "behalf" with trust shaped by these words, not by a vague optimism outside the passage.