2 Corinthians 5:21

For--omitted in the oldest manuscripts. The grand reason why they should be reconciled to God, namely, the great atonement in Christ provided by God, is stated without the "for" as being part of the message of reconciliation (Co2 5:19). he--God. sin--not a sin offering, which would destroy the antithesis to "righteousness," and would make "sin" be used in different senses in the same sentence: not a sinful person, which would be untrue, and would require in the antithesis "righteous men," not "righteousness"; but "sin," that is, the representative Sin-bearer (vicariously) of the aggregate sin of all men past, present, and future. The sin of the world is one, therefore the singular, not the plural, is used; though its manifestations are manifold (Joh 1:29). "Behold the Lamb of God, that taketh away the SIN of the world." Compare "made a curse for us," Gal 3:13. for us--Greek, "in our behalf." Compare Joh 3:14, Christ being represented by the brazen serpent, the form, but not the substance, of the old serpent. At His death on the cross the sin-bearing for us was consummated. knew no sin--by personal experience (Joh 8:46) [ALFORD]. Heb 7:26; Pe1 2:22; Jo1 3:5. might be made--not the same Greek as the previous "made." Rather, "might become." the righteousness of God--Not merely righteous, but righteousness itself; not merely righteousness, but the righteousness of God, because Christ is God, and what He is we are (Jo1 4:17), and He is "made of God unto us righteousness.

— Jamieson-Fausset-Brown Commentary (public domain)