Faith alone?
One essential difference which divides Catholics and many Protestants is the question of faith and works in salvation. The disagreement began at the Reformation. In fact, the “material principle” of the Reformation was that we are saved “Sola Fide”, by “Faith Alone” and that works have no place in our justification whatsoever.
This subject often comes up when speaking with Protestants. I think most Catholics have had the experience at one point or another of being told by a Protestant that Catholicism doesn’t preach the Gospel, teaching instead that we have to earn our salvation. St. Paul’s epistles to the Romans and Galatians are often cited during such an exchange.
When this has happened to me in the past, I tend not to dwell too long upon the person’s interpretation of Paul’s epistles. I usually simply point out that in those letters St. Paul is contrasting faith in Christ with the works of the Mosaic Law. I turn then to the Epistle of James, since it presents a bit of a problem if someone wishes to say we’re saved by faith alone…