Galatians 1:7
which is not even a gospel. Evidently some people are troubling you and trying to distort the gospel of Christ.
What it says
But this is not really another gospel, Paul says, only a distortion spread by people who are troubling them.
What it is doing
It defines the false gospel as corruption of the true one.
In context
6I am amazed how quickly you are deserting the One who called you by the grace of Christ and are turning to a different gospel — 7which is not even a gospel. Evidently some people are troubling you and trying to distort the gospel of Christ. 8But even if we or an angel from heaven should preach a gospel contrary to the one we preached to you, let him be under a curse! 9As we have said before, so now I say again: If anyone is preaching to you a gospel contrary to the one you received, let him be under a curse!