Do Reformed Protestants and Roman Catholics understand grace differently?

Yes, Reformed Protestants and Roman Catholics understand grace differently.

Roman Catholic theology, especially in the later Middle Ages, tended to speak of grace as though it were a substance. Many Reformed Christians use the language “means of grace” when we speak about the Word of God and the sacraments. That language is actually a hangover from the medieval period when, if you wanted the grace of God, the means by which you received that grace was the seven sacraments.

In medieval Roman Catholic theology, grace was essentially packaged in the sacraments. For example, in baptism, grace would be infused into you. Grace was made to be a kind of abstract commodity and was formulated almost exclusively in terms of the sacraments. Without the sacraments, you couldn’t get grace. In a very paradoxical way—I am not sure all Protestants appreciate this—medieval theology was actually all about how you get grace. However, they misunderstood what grace is and packaged it in sacramental terms.

The breakthrough for Luther, Calvin, and the earlier Reformers came as they recognized that grace isn’t a commodity that one person, by virtue of his ordination, can pass to another person. The grace of God is actually found in Jesus Christ. Grace is found in a person. You do not need sacraments to receive the grace of God; you need Jesus Christ. This resulted in a clearer understanding of justification.

In the Roman Catholic system, you would receive grace at baptism, which you could mess up, and then you would need the other sacraments to build you up and infuse more righteousness in you. Eventually, once your faith became so suffused with love that you were actually righteous, God could justify you. Luther discovered that, as long as that paradigm stood, you could never be sure of your justification because you could never be sure that you’ve done enough to be justified.

Luther’s revolution was to discover that grace is not an infused substance that can be topped up to make you justifiable. Rather, Jesus Christ is the grace of God to you, and when you have Christ, you’re immediately, perfectly, and finally justified. You are not fully sanctified, but the liberation of Luther’s discovery was absolutely phenomenal because they understood that when the Scriptures speak about the grace of God, they’re speaking ultimately about the Lord Jesus Himself and about faith in Him.