From The Future of Justification (Piper, John. The Future of Justification A Response to N. T. Wright. New York: Crossway Books, 2007).
Piper is discussing how God's righteousness should be defined. He begins with a 'simple' definition: "The simple way is to say that God’s righteousness consists in his unswerving commitment to do what is right." (63)
Piper, however, recognizes that this definition, though true, may not be satisfying.
"It is not very satisfying simply to say that God’s righteousness is his commitment to do what is right, because it leaves the term “right” undefined. We don’t feel like we have gained very much in defining “righteousness” if we use the word “right” to define it." (63)
And this definition, according to Piper, may not be ultimately satisfying because it leads one to questions such as these: “How does God decide what is right? Who tells God what is right? Is there a book of laws or rules that God has to obey?” ((63) The answer to these questions is where Piper is heading, "Answering those questions gets at the deeper meaning of righteousness. What is the “right” to which God is unswervingly committed?" (64)
And the following is the conclusion, written as only Piper can write it, to the investigation into God's righteousness:
The answer is that there is no book of laws or rules that God consults to know what is right. He wrote the book. What we find therefore in the Old Testament and in Paul is that God defines “right” in terms of himself. There is no other standard to consult than his own infinitely worthy being. Thus, what is right, most ultimately, is what upholds the value and honor of God—what esteems and honors God’s glory.
The reasoning goes like this: The ultimate value in the universe is God—the whole panorama of all his perfections. Another name for this is God’s holiness (viewed as the intrinsic and infinite worth of his perfect beauty) or God’s glory (viewed as the out-streaming manifestation of that beauty). Therefore, “right” must be ultimately defined in relation to this ultimate value, the holiness or the glory of God—this is the highest standard for “right” in the universe. Therefore, what is right is what upholds in proper proportion the value of what is infinitely valuable, namely, God. “Right” actions are those that flow from a proper esteem for God’s glory and that uphold his glory as the most valuable reality there is. This means that the essence of the righteousness of God is his unwavering faithfulness to uphold the glory of his name. And human righteousness is the same: the unwavering faithfulness to uphold the glory of God. (64)