The difference between Catholics and Protestants is that they see faith as something that they can measure. Therefore, they claim to be saved by faith alone. I'm reminded of the question that faith alone people ask faith and works people. "How many works do you need to perform to be saved?" There are faith and works people outside of Catholicism. So, I don't know how they feel about this question. But I can tell you that the question is completely foreign to Catholics, because we are taught not to judge our faith nor our works. We leave the question of who is saved, to God.
Faith alone people suffer with two false assumptions.
1. That they have the right to declare themselves saved.
2. That they have the ability to measure their faith.
Thus, they assume that everybody lives with those assumptions. But we, Catholics, don't. The proof is vey easy to discover. Ask a Catholic, any Catholic, whether he is saved. His answer will invariably be, "I don't know." Why? Because God is our Judge.
1 Corinthians 4:4 I am not conscious of anything against me, but I do not thereby stand acquitted; the one who judges me is the Lord. 5 Therefore, do not make any judgment before the appointed time, until the Lord comes, for he will bring to light what is hidden in darkness and will manifest the motives of our hearts, and then everyone will receive praise from God.
The reason that faith alone people ask this question is be cause they are used to judging themselves saved. Even though this is an unbiblical attitude. But, the question can easily be turned around on them. I ask them in turn, "How much faith do you need in order to be saved and how do you measure it? Can you read anyone's heart? Can you even read your own?" Here's what Scripture says on that question:
Jeremiah 17: More torturous than anything is the human heart, beyond remedy; Who can understand it? 10 I, the LORD, explore the mind; and test the heart, Giving to all according to their ways, according to the fruit of their deeds
As for me, I don't even try to read my own heart nor anyone else's. I leave that to God.