A fair number of pixels have been lit up over the issue of how 2 Corinthians 5:21 is to be interpreted, and specifically how this relates to our understanding of justification. N. T. Wright has an interesting article on how “the righteousness of God” should be understood in this passage. This article was dismissed by Adrian Warnock as “wholly unconvincing” though he fails to tell us why.
Somewhat more interesting is Piper’s response to the article in his book The Future of Justification. (A PDF of the book is available here.) In the introduction he calls the article “one of the most eccentric articles in all his work” (p. 24). He dedicates chapter 11 to a response.
There is a fundamental assumption that Piper makes, that there is one, and only one way to understand justification. For him, justification is a fact, not a metaphor. It is the core reality. Metaphors can be used to describe it, but it is the real thing. I emphasize this repeatedly, because it underlies many of the arguments that Piper makes. For him, it would be quite inadequate to suggest that a different metaphor was in play in a different verse, and thus perhaps it might be understood differently.