Paul is astonished that the Galatians are so quickly deserting the gospel for a distorted counterfeit, and pronounces a curse on anyone, even an angel, who preaches a different one. From there the sermon traces the word “gospel” itself: in the Roman Empire, “euangelion” announced good news of a king’s ascension or victory; in Isaiah, God had already promised good news of release, comfort, and the coming of His reign. Jesus is that good news in person, not merely a messenger of it.
The message pushes past mere definition toward response: the gospel is a Person to be loved, not just a message to be understood, and its truth has been worth dying for, as it was for the martyr Polycarp, who would not deny his King of eighty-six years. The aim is not simply to understand the gospel accurately, but to see its glory clearly enough that, having it, a person wants nothing else.