Paul is addressing the believers with a sense of urgency and surprise because they are quickly moving away from the teachings of Christ. This shift is not just a minor deviation but a turning towards a completely different gospel, which Paul implies is not the true gospel at all. The core of the Christian message is the grace of Christ, which offers salvation and reconciliation with God. By turning to another gospel, the believers risk losing the essence of their faith.
Paul's astonishment underscores the importance of vigilance in faith. It serves as a cautionary tale about the allure of teachings that may seem appealing but ultimately lead away from the truth. The verse calls believers to remain rooted in the grace they have received, which is the unmerited favor of God through Jesus Christ. This grace is not earned by works but is a gift that transforms lives. The message is timeless, urging Christians to discern and hold fast to the foundational truths of their faith, resisting any teaching that contradicts the gospel of grace.