my son-in-law is Missouri Synod Lutheran. He wants to know why we believe in the authority of the Pope.
The following links should help answer your question about papal authority. If you have any further questions, please contact Catholic Answers directly.
The Authority of the Pope Part 1 by the Early Church Fathers
The Authority of the Pope Part 2 by the Early Church Fathers
How Do We Know It’s the True Church? Twelve Things to Look For by Fr. Dwight Longenecker