What does the Bible teach about another gospel?

In Galatians 1:6-9, Paul expresses astonishment that believers would turn to a different gospel, stating that there is no other gospel than the one he preached. Any alteration that adds works to the grace of Christ fundamentally changes the message. Paul then pronounces a curse on anyone, whether he himself or an angel from heaven, who preaches a gospel contrary to what was originally given. This emphasizes the seriousness of adhering to the true gospel, which relies solely on Christ's completed work for salvation, affirming that all other gospels will lead to condemnation.