Here’s a very insightful post from Lee Irons critiquing the theory that “righteousness” means “covenant faithfulness”. I’ll quote a sizeable chunk of Irons’ conclusions because they’re highly relevant to both of my series on righteousness and covenant:
As you can see, the New Perspective claim that “the righteousness of God” is a cipher denoting “God’s saving faithfulness to his covenant” rests on the outdated Lowthian theory of Hebrew synonymous parallelism. Rather than equating “righteousness” with “faithfulness” (or “salvation”), it is better to see the instances in the Psalms and Isaiah where these terms are used in parallelism as “binoculars” in which these different concepts mutually interpret one another and lead to a picture that is larger than the sum of its parts.
God’s salvation is the result of his faithfulness to his covenant with Abraham. God’s salvation is also an expression of his righteousness, because he executes salvation in a manner that is consistent with his justice and holiness; indeed, salvation itself is an essentially judicial activity, for salvation comes through judgment. For example, at the Exodus, God’s deliverance of his people was accomplished by judgment on the Egyptians. At the cross, salvation was accomplished because the judgment we deserved was borne by Jesus as our substitute.
In other words, when “God’s salvation” or “God’s faithfulness” and “God’s righteousness” are found in parallel, the conclusion we are to draw is not that the word “righteousness” itself means “salvation” or “faithfulness,” but that God’s saving activity comes in fulfillment of his covenant promises and is an expression of his righteousness. Especially in those cases where “salvation” and “righteousness” are parallel (see, e.g., Psalm 98:2; Isaiah 51:5-8; 56:1), the point is that God’s salvation has a strongly judicial dimension.
To conclude, the static Lowthian theory of synonymous parallelism has been superceded in the last 30 years by a more nuanced understanding, and this scholarly shift in the interpretation of Hebrew poetry undermines one of the pillars of the NPP. When properly understood, Hebrew parallelism provides no support for the theory that δικαιοσύνη θεοῦ is a cipher for God’s faithfulness to his covenant.