I was talking with a philosopher friend of mine who is Roman Catholic about the differences between Catholic and Protestant views on salvation and justification, and he said something that I'd never heard before. If he's right, this should make the Catholic view much more palatable to Protestants. He explained the Catholic view as follows. Salvation is initiated by a work of God's grace, an unearned, unmerited favor of God. Then we are brought to what Protestants typically call sanctification over the rest of our lives in this world, and at the end God judges the works that his grace produced in our lives to be meritorious. We actually earn our salvation. This comes only through the work of God in our lives, and thus this is what Reformed theologians tend to call monergistic. God does all the work, and we do it only because he is doing it in us. But that doesn't mean we aren't doing it. This involves compatibilism about human freedom and divine sovereignty. Synergism would mean God does part of the work, while we do the rest. That's not the Catholic view. The Catholic position is that God does all of it, and we also do all of it. In other words, the Catholic position on that is the same as that of Reformed Protestants. The only difference is that Catholics think that should count as enough to say we merit or deserve reward.
None of this was new to me, since I've written a great deal on this before. But I was pressing him on why he thought that should count as merit. His answer made a great deal of sense. When God promises something, he bestows on us a right that we wouldn't otherwise have. We now are owed something. He makes it the case that we deserve something. When he says that we will have a reward for doing something, and we do that thing, then he owes us that thing. He gives us the right to it. He makes it such that anyone who fulfills the command in question has earned the reward in question. It's conditional merit, since what makes it merit is that God promised something. It wouldn't be merit without that promise, and God had no obligation to promise it. But given that God promised it, God has an obligation to follow through on that promise and treat the actions in question as meriting the reward in question. Now maybe my friend completely misunderstands the Catholic view, but he's a pretty smart guy with a lot of philosophical training to make careful distinctions, and this is how he understands the Catholic view after having investigated it very carefully. If he's right, I'm not sure Protestants have anywhere near as serious an objection as we might otherwise have thought.