And if grace ... - If the fact that any are reserved be by grace, or favor, then it cannot be as a reward of merit. Paul thus takes occasion incidentally to combat a favorite notion of the Jews, that we are justified by obedience to the Law. He reminds them that in the time of Elijah it was because God had reserved them; that the same was the case now; and therefore their doctrine of merit could not be true; see Romans 4:4-5; Galatians 5:4; Ephesians 2:8-9.
Otherwise grace ... - If people are justified by their works, it could not be a matter of favor, but was a debt. If it could be that the doctrine of justification by grace could be held and yet at the same time that the Jewish doctrine of merit was true, then it would follow that grace had changed its nature, or was a different thing from what the word properly signified. The idea of being saved by merit contradicts the very idea of grace. If a man owes me a debt, and pays it, it cannot be said to be done by favor, or by grace. I have a claim on him for it, and there is no favor in his paying his just dues.
But if it be of works ... - “Works” here mean conformity to the Law; and to be saved by works would be to be saved by such conformity as the meritorious cause. Of course there could be no grace or favor in giving what was due: if there was favor, or grace, then works would lose their essential characteristic, and cease to be the meritorious cause of procuring the blessings. What is paid as a debt is not conferred as a favor.
And from this it follows that salvation cannot be partly by grace and partly by works. It is not because people can advance any claims to the favor of God; but from his mere unmerited grace. He that is not willing to obtain eternal life in that way, cannot obtain it at all. The doctrines of election, and of salvation by mere grace, cannot be more explicitly stated than they are in this passage.