When Paul expressed astonishment that the Galatians were turning to a different gospel (Gal 1:6), he didn’t want them to wrongly conclude that he was actually acknowledging other gospels as legitimate. This concern led him to quickly add, “not that there is another one, but there are some who trouble you and want to distort the gospel of Christ” (1:7).
For Paul, the gospel is the message about Christ, and there is no other legitimate gospel for sinners. Other messages distort the true gospel. Put another way, other messages lead to a false understanding of Christ and salvation.
Christians must beware of falsehoods that smell good and look genuine. Our five senses do not detect deception, so we need to pray for discernment from the Holy Spirit and cultivate a love for the truth of God’s Word.
There is no other legitimate gospel other than the good news about Jesus Christ. All other messages are illegitimate and powerless to save–thus, those messages are bad news masquerading as something worth believing.