How do we know the authority of Paul as an apostle?

The authority of Paul as an apostle is evident from the circumstances surrounding his calling and the significant role he plays in the spread of the Gospel among Gentiles. As stated in 1 Corinthians 9:1, Paul emphasizes that he has seen Jesus Christ, which is a requirement for apostolic legitimacy. Moreover, Paul's letters contain a recurring emphasis on the Gospel's power to transform lives, underlining a divine endorsement of his role. His steadfastness amidst persecution and the establishment of various churches further contribute to recognizing his authority. Paul's unique experience of directly encountering the risen Christ legitimizes his apostolic claims and affirms his role in God's plan of salvation.