Another subject of perennial debate is the meaning of the phrase δικαιοσύνη θεοῦ, "the righteousness of God," as it appears in Paul's letter to the Romans (e.g., at 3.21). Some persons think of it as "a righteousness from God," believing it a reference to the imputation of Christ's righteousness acquired by faith. N.T. Wright understands in the phrase, however, a reference to God's covenant faithfulness. This has proven to be a controversial proposal. I am sympathetic to some extent, but I prefer Campbell's interpretation in The Deliverance of God (Eerdmans, 2009), namely that Paul means God's righteous act of deliverance.
One argument that won't work against Wright's proposal is a facile and puerile appeal to the lexicon. Yes, it is obvious that when you open up BDAG, δικαιοσύνη means "righteousness" and not "covenant faithfulness." Wright doesn't mean to offer so easily refutable a claim as that, however, as if he weren't himself aware of the typical lexical definition of the term. The point is rather that what Paul really means to get across by the term is something beyond the composition of the lexical definition of either item. Rather, when Paul refers literally to "God's righteousness," this phrase is more deeply understand as "God's faithfulness to his covenant."
In other words, the objection from the lexicon assumes that Paul doesn't mean anything more by these terms than merely to combine what the terms typically mean in other contexts. This is a bad objection because this is precisely the point Wright denies. He spends a lot of time demonstrating how the notion of covenant was a ubiquitous notion in Jewish thinking, how it was always in the background, how it was an essential component of the lens by which they interpreted the world. If this is right, then Wright has plenty of reason to suppose Paul does not merely mean to combine the two terms' ordinary lexical meanings when he writes about the "righteousness of God" in Romans.
Now my point is not to argue in favor of Wright's proposal but merely to defend it against a puerile objection. Like I said, I prefer Campbell's reading of δικαιοσύνη θεοῦ as "the deliverance of God," or "God's righteous act of deliverance." Campbell, too, supposes that the full meaning of the phrase as Paul intends it to be understood carries more than just the lexical definitions of either terms. In support of Campbell's reading and this critical supposition, I wish to point out a possible background source for Paul's phrase.
In Isa 51.5-6, 8 we find three uses of the word "righteousness" in parallelism with "salvation":
My righteousness draws near speedily, my salvation is on the way. . .
. . . But my salvation will last forever, my righteousness will never fail. . . .
. . . But my righteousness will last forever, my salvation through all generations.
The parallelism suggests that the two terms are being used in a roughly synonymous way. Now it is clear that "salvation" in this context refers to some concrete act of deliverance that God is going to effect for the Jews in exile in Babylon. That is obviously what the prophet would have been talking about when he made public reference to salvation -- to some event in history, orchestrated and effected by God, which results in the deliverance of the Jewish people.
Evidently the Isaian prophet can speak of "God's righteousness" to refer to the same event, the same concrete circumstances of deliverance. This is because they have been accomplished because of God's righteousness; therefore he refers to them as God's righteousness, even though he is not talking about God's character trait so much as some things that have or will happen in history. This is called metonymy -- using the name of one thing to describe another. (This happens all the time; for instance, we refer to business executives as "suits.") The NRSV, picking up on the parallelism, directly translates "righteousness" in all these cases as "deliverance."
My suggestion in favor of Campbell's interpretation is that Paul's use of δικαιοσύνη θεοῦ is borrowed metonymy from Isa 51. In other words, Paul uses the phrase δικαιοσύνη θεοῦ to refer to an act of deliverance accomplished by God in his righteousness, namely the deliverance that came about by Christ.
This suggestion is already plausible because of the well-recognized significance that Isaiah has for New Testament theology. Mark says that the things which happened to Jesus are the fulfillment of the prophet Isaiah (Mk 1.2), and in Luke 4 Christ identifies his mission with that of Isa 61. Furthermore there are a number of aspects of the Isa 51 text that are relevant for Paul: there is the pursuit of righteousness (v. 1); there is mention of Abraham and Sarah, blessed by God (v. 2); there is mention of the restoration to prelapsarian conditions (v. 3); there is mention of teaching and light for the nations (v. 4); there is mention of the removal of God's wrath (vv. 17, 21-22). I think, then, that Isa 51 offers us a plausible source and context for Paul's use of the phrase δικαιοσύνη θεοῦ, and Campbell offers us the right interpretation of it.