Recently, as I was reading through 2 Corinthians 5-6, it became evident that critiques of the traditional Reformed reading of 2 Corinthians 5.21 have some merit. In v. 21 Paul wrote, “For our sake he made him to be sin who knew no sin, so that we in him might become the righteousness of God.” I have read v. 21 as referring to Christ becoming sin in exchange for us as we become the righteousness of God. In other words this is a form of substitutionary atonement soteriology. Christ takes on our sins; we take on his righteousness. While I still strongly affirm substitutionary atonement it is not apparent that this passage is referring to such a thing.
The one thing that stands against the Reformed reading of this verse is that contextually the first person plural has been referring to Paul and his coworkers in the gospel. Since 4.1 Paul has spoken of his partners in ministry. Whenever he refers to the Corinthians it seems to be in the second person plural. The Corinthians are not brought over to Paul’s side of things until about 6.11. Therefore, when he says “that we might become the righteousness of God” in v. 21 it appears he would need to shift “us” language from referring exclusively to himself and his coworkers to referring to the Corinthians as well only to shift back into “us” and “you” language, excluding the Corinthians once again, in 6.1.
N.T. Wright understands “righteousness” to refer to “covenant-faithfulness”. Therefore, according to Wright, Paul is saying, “…in the Messiah, we might embody God’s faithfulness, God’s covenant faithfulness, God’s action in reconciling the world to himself.”  This would explain, in part, why the righteousness would refer to Paul and his coworkers and not the Corinthians if indeed we cannot read the Corinthians as being included in “we”. Nevertheless, I am not sure if his reasoning suffices.
For those who see this passage as referring to imputation why do you continue to read the passage this way? For those who see it as Wright sees it why do you agree with his reading? If you have another understanding of 5.21 please share.
 Justification: God’s Plan and Paul’s Vision, 163. Elsewhere in this book as well as some other books, lectures, and so forth, Wright gives his arguments for understanding “righteousness” to refer to covenantal faithfulness. I will not try to reproduce those here.