Christ Alone
As complicated as Rome's view of salvation may be, her debate with the Reformer's came down to one word: "alone". Sure, Rome believed that salvation was based upon the work of Christ, but she would not say that salvation was based upon the work of Christ alone. Christ alone, or solus Christus in Latin, may seem like a very small difference; one word! But for the Reformer's, it was all the difference in the world. Upon this one word (alone) the whole gospel depended.