Adam Clarke's Commentary on the Bible: 2 Corinthians 5:21
For he hath made him to be sin for us - Τον μη γνοντα ἁμαρτιαν, ὑπερ ἡμων ἁμαρτιαν εποιησεν· He made him who knew no sin, (who was innocent), a sin-offering for us. The word ἁμαρτια occurs here twice: in the first place it means sin, i.e. transgression and guilt; and of Christ it is said, He knew no sin, i.e. was innocent; for not to know sin is the same as to be conscious of innocence; so, nil conscire sibi, to be conscious of nothing against one’s self, is the same as nulla pallescere culpa, to be unimpeachable.
In the second place, it signifies a sin-offering, or sacrifice for sin, and answers to the חטאה chattaah and חטאת chattath of the Hebrew text; which signifies both sin and sin-offering in a great variety of places in the Pentateuch. The Septuagint translate the Hebrew word by ἁμαρτια in ninety-four places in Exodus, Leviticus, and Numbers, where a sin-offering is meant; and where our version translates the word not sin, but an offering for sin. Had our translators attended to their own method of translating the word in other places where it means the same as here, they would not have given this false view of a passage which has been made the foundation of a most blasphemous doctrine; viz. that our sins were imputed to Christ, and that he was a proper object of the indignation of Divine justice, because he was blackened with imputed sin; and some have proceeded so far in this blasphemous career as to say, that Christ may be considered as the greatest of sinners, because all the sins of mankind, or of the elect, as they say, were imputed to him, and reckoned as his own. One of these writers translates the passage thus: Deus Christum pro maximo peccatore habuit, ut nos essemus maxime justi, God accounted Christ the greatest of sinners, that we might be supremely righteous. Thus they have confounded sin with the punishment due to sin. Christ suffered in our stead; died for us; bore our sins, (the punishment due to them), in his own body upon the tree, for the Lord laid upon him the iniquities of us all; that is, the punishment due to them; explained by making his soul - his life, an offering for sin; and healing us by his stripes.
But that it may be plainly seen that sin-offering, not sin, is the meaning of the word in this verse, I shall set down the places from the Septuagint where the word occurs; and where it answers to the Hebrew words already quoted; and where our translators have rendered correctly what they render here incorrectly. In Exodus, Exo 29:14, Exo 29:36 : Leviticus, Lev 4:3, Lev 4:8, Lev 4:20, Lev 4:21, Lev 4:24, Lev 4:25, Lev 4:29, Lev 4:32-34; Lev 5:6, Lev 5:7, Lev 5:8, Lev 5:9, Lev 5:11, Lev 5:12; Lev 6:17, Lev 6:25, Lev 6:30; Lev 7:7, Lev 7:37; Lev 8:2, Lev 8:14; Lev 9:2, Lev 9:3, Lev 9:7, Lev 9:8, Lev 9:10, Lev 9:15, Lev 9:22; Lev 10:16, Lev 10:17, Lev 10:19; Lev 12:6, Lev 12:8; Lev 14:13, Lev 14:19, Lev 14:22, Lev 14:31; Lev 15:15, Lev 15:30; Lev 16:3, Lev 16:5, Lev 16:6, Lev 16:9, Lev 16:11, Lev 16:15, Lev 16:25, Lev 16:27; Lev 23:19 : Numbers, Num 6:11, Num 6:14, Num 6:16; Num 7:16, Num 7:22, Num 7:28, Num 7:34, Num 7:40, Num 7:46, Num 7:52, Num 7:58, Num 7:70, Num 7:76, Num 7:82, Num 7:87; Num 8:8, Num 8:12; Num 15:24, Num 15:25, Num 15:27; Num 18:9; Num 28:15, Num 28:22; Num 29:5, Num 29:11, Num 29:16, Num 29:22, Num 29:25, Num 29:28, Num 29:31, Num 29:34, Num 29:38.
Besides the above places, it occurs in the same signification, and is properly translated in our version, in the following places: -
2 Chronicles, 2Ch 29:21, 2Ch 29:23, 2Ch 29:24 : Ezra, Ezr 6:17; Ezr 8:35 : Nehemiah, Neh 10:33 : Job, Job 1:5 : Ezekiel, Eze 43:19, Eze 43:22, Eze 43:25; Eze 44:27, Eze 44:29; Eze 45:17, Eze 45:19, Eze 45:22, Eze 45:23, Eze 45:25. In all, one hundred and eight places, which, in the course of my own reading in the Septuagint, I have marked.