Roman Catholics believe they must do good to get to heaven.  Protestants believe that doing good has resulted in at least one person being given the opportunity to get to heaven (Cornelius in Acts 10), who, then, took advantage of that opportunity.

The difference is that Roman Catholics believe that a person can, regardless of whether Cornelius-wise or not, obtain heaven by the good that they do.  Protestants believe that a person can, Cornelius-wise, gravitate (move) toward heaven by the good that they do.  The Roman Catholic belief is “if you do enough good, regardless of whether Cornelius-wise or not, you will be given heaven.”  The Protestant belief is “if you do good, Cornelius-wise, you will be given an opportunity to be given heaven.”

The Roman Catholic belief is not in the Bible.  The Protestant belief is in the Bible.

If you need more explanation, read Acts 10 in the Bible (KJV or IAV).  We also now provide a more recent and powerful discussion of faith and works at Faith and Works on our church website.