Moo’s introductory analysis of this section has several good points:
[The questions in vv. 14–23] state the inevitable human response to an insistence on the sovereignty of God in salvation: if God decides apart from anything in the human being whom he will choose and whom he will reject (v. 13), how can he still be “righteous” (v. 14) — and how can he blame people if they reject him (v. 19)?
Paul responds to the first question with citations of and comments on Scripture (vv. 15–18) and to the second with a series of rhetorical questions (vv. 20–23). These responses are not what we might expect. Paul does not attempt to show how God’s choice of human beings for salvation fits with their own choosing of God in faith. Quite the contrary: rather than compromising the apparent absolute and unqualified nature of God’s election, he reasserts it in even stronger terms. God not only has mercy on whomever he wants, he also hardens whomever he wants (v. 18). God’s freedom to act in this way, Paul suggests, while directed toward a definite end (vv. 22–23), is the freedom of the Creator toward his creatures, and cannot be qualified (vv. 20–21). Many commentators are troubled by Paul’s apparent disregard for human choice and responsibility. Dodd criticizes the argument here as “a false step.” O’Neill goes further, claiming the teaching is “thoroughly immoral,” and follows a number of the church fathers in ascribing the offending verses to someone other than Paul. These criticisms are sometimes the product of a false assumption: that Paul’s justification of the ways of God in his treatment of human beings (his “theodicy”) must meet the standard set by our own assumptions and standards of logic. Paul’s approach is quite different. He considers his theodicy to be successful if it justifies God’s acts against the standards of his revelation in Scripture (vv. 15–18) and his character as Creator (vv. 20–23). In other words, the standard by which God must be judged is nothing less and nothing more than God himself.
— The Letter to the Romans, 2nd ed, pp. 610–611
Fn. 196: “…C. Müller notes that Greek theodicies usually dealt with God’s ‘righteousness’ in the context of a general norm of ‘fairness,’ while Paul answers the question of God’s ἀδικία [injustice] with an assertion of God’s ἐξουσία (‘authority’) (Gottes Gerechtigkeit, 84–85).”
For a list of all of my posts on Douglas Moo’s commentary on Romans, see here.