How do you respond to Romans 9:18?
“[God] has mercy on whomsoever he chooses, and he hardens the heart of whomsoever he chooses.”
This is one of the most frequently cited texts in support of Calvinism. If the text implied that whether or not people were believers was a result of whether God had mercy on them or hardened them, they would have a point. But if read in context, the passage rather suggests that God has mercy and hardens people in response to what they do.
Hence Paul summarizes his argument in chapter 9 by noting that Gentiles received the righteousness of God because they had faith while unbelieving Jews were hardened “[b]ecause they did not strive for [righteousness]…on the basis of faith, but as if it were based on works” (30–32, emphasis added). “They were broken off because of their unbelief…” (11:20, emphasis added, cf. 10:3). This is why they as a nation have now been hardened (Rom. 11:7, 25) while the Gentiles who seek God by faith have been “grafted in” (11:23).
To Jews who assumed that their standing before God was based on their works and/or their nationality, this seems arbitrary (9:14, 19). But Paul insists that God has the right to have mercy on people simply because of their faith if he so chooses. “[H]e has mercy on whomsoever he chooses, and he hardens the heart of whomsoever he chooses.”
For a more extensive discussion of Romans 9, see How do you respond to Romans 9?