How do we know that Paul received the gospel by revelation?

In Galatians 1:11-12, Paul emphasizes that the gospel he preached was not of human origin but was revealed to him directly by Jesus Christ. This was critical for establishing his authority as an apostle, especially since he was not among the original disciples of Christ. He highlights that the truth of the gospel cannot be comprehended by human wisdom alone and requires divine revelation. Therefore, the authenticity of his message comes from his firsthand divine encounter, which he firmly states to reinforce the gospel's credibility in the face of opposition.