What does the Bible say about the authority of Paul as an apostle?

In his epistle to the Galatians, Paul defends his apostolic authority by stating that he was called neither by men nor through men, but directly by Jesus Christ and God the Father. This claim underscores the divine nature of his calling, asserting that his gospel is not of human origin. In Galatians 1:1, he emphasizes that this unique calling establishes his authority in proclaiming the Gospel, distinct from those who are called by human endorsement. The significance of this assertion is to combat the false apostles who sought to undermine his ministry by claiming superiority based on their human connections to the original apostles.