He made Christ who knew no sin to [judicially] be sin on our behalf, so that in Him we would become the righteousness of God [that is, we would be made acceptable to Him and placed in a right relationship with Him by His gracious lovingkindness].
For our sake He made Christ [virtually] to be sin Who knew no sin, so that in and through Him we might become [endued with, viewed as being in, and examples of] the righteousness of God [what we ought to be, approved and acceptable and in right relationship with Him, by His goodness].
This means that our knowledge of men can no longer be based on their outward lives (indeed, even though we knew Christ as a man we do not know him like that any longer). For if a man is in Christ he becomes a new person altogether—the past is finished and gone, everything has become fresh and new. All this is God’s doing, for he has reconciled us to himself through Jesus Christ; and he has made us agents of the reconciliation. God was in Christ personally reconciling the world to himself—not counting their sins against them—and has commissioned us with the message of reconciliation. We are now Christ’s ambassadors, as though God were appealing direct to you through us. As his personal representatives we say, “Make your peace with God.” For God caused Christ, who himself knew nothing of sin, actually to be sin for our sakes, so that in Christ we might be made good with the goodness of God.
The one who in his person had no da’as of chattat (sin) [Ac 3:14; Yn 8:46; MJ 4:15; 7:26; 1K 2:22; 1Y 3:5], this one Hashem made a chattat sin offering [Ga 3:13; YESHAYAH 53:10; VAYIKRA 4:24 TARGUM HASHIVIM] on our behalf that we might become the Tzidkat Hashem [DANIEL 9:24] in Moshiach. [1C 1:30; Pp 3:9] [T.N. In this next chapter Rav Sha’ul warns against associations or worldly influences or fascinations that will contaminate the believer, who should not think he can have both the world’s evil pleasures and the House of G-d’s holy chelek.]