What is the biggest difference between Catholics and Protestants?

Catholics and Protestants share the historic core of Christian faith: one God in three persons, Jesus as God's Son who died and rose again, the Bible as God's inspired word. The biggest difference is really about authority and how a person is made right with God.

Catholics believe final authority rests in Scripture together with sacred Tradition, interpreted through the Church's teaching office, led by the Pope. Most Protestants hold Scripture alone as the final authority above any church tradition or leader.

On salvation, Catholic teaching holds a person is justified through grace working together with faith, expressed especially through the sacraments. Most Protestants teach justification is by faith alone—a decisive declaration the moment someone trusts Christ, with good works following as evidence rather than a cause.

Both sides agree grace is essential, and both genuinely value good works. They disagree about exactly how grace, faith, and the sacraments fit together.