Paul knows how his readers will react to what he has just said. If God chose Jacob over Esau before they were born, "not of works, but of him that calleth" (Romans 9:11), is God being unfair? Barnes frames the question as, "Does God do injustice or wrong?" and notes that this charge has often been brought against the doctrine. Gill says Paul raises an objection that is "not an objection of his own, but of an adversary," so that he can answer it. Paul puts the hardest question on the table himself rather than avoiding it.

Paul answers at once: "God forbid" (Romans 9:14). Then he lets God's own words speak. To Moses God said, "I will have mercy on whom I will have mercy, and I will have compassion on whom I will have compassion" (Romans 9:15). Paul concludes, "it is not of him that willeth, nor of him that runneth, but of God that sheweth mercy" (Romans 9:16).

"God forbid" translates the Greek me genoito, literally "may it not be." It is Paul's strongest way of rejecting an idea, and Barnes points back to Romans 3:4, where Paul uses it the same way. Gill says Paul answers "by way of detestation and abhorrence." Paul uses the same pattern of question and answer often in Romans, for example "What shall we say then? Shall we continue in sin, that grace may abound? God forbid" (Romans 6:1-2). The quotation in Romans 9:15 comes from Exodus 33:19, where God speaks to Moses about His goodness and His name.

This question is about God's character. Paul does not answer by putting God on trial; he answers by letting God define Himself. In Exodus 33:19, God's words about showing mercy come as He promises to make His goodness pass before Moses. Mercy, by definition, is not owed. Matthew Henry writes, "Whatever God does, must be just."

Gill adds that God's choosing is "neither an act of justice, nor injustice" but of grace. That is why Paul can say "God forbid" so firmly. No one is wronged when God shows undeserved mercy to someone else.