The sermon notes discuss Paul defending his calling and the true gospel in his letter to the Galatians. Paul asserts that he received his calling directly from God, not from men or other apostles, and that the gospel he preaches is the one given to him by God. The sermon examines how Paul establishes his credentials to the Galatian believers and reiterates that salvation comes through faith in Christ alone, not by following Jewish laws and traditions. The application encourages believers to share their testimony of God's grace and proclaim the true gospel so that others may come to faith and glorify God.