“This is illuminating. If you add anything to Christ as a requirement for acceptance with God—if you start to say: To be saved I need the grace of Christ plus something else—you completely reverse the “order” of the gospel and make it null and void. Any revision of the gospel reverses it. That is why in verse 6 Paul says that the false teachers are producing “a different gospel”, which he quickly qualifies in verse 7 as “really no gospel at all."
- Tim Keller, Galatians For You