Religious leaders, claiming to know and understand how a person becomes righteous (forgiven, clean, pure, and accepted by God), infiltrated the Galatian churches to undo what Paul taught about how a person becomes righteous.
They taught righteousness was through faith in Jesus plus following the days, diets, duties, and demands of the law of Moses (a moral and religious system).
Paul taught righteousness was by grace (what Jesus did for us in dying for our sins) through faith in Jesus, apart from any works.
In Galatians 1:7, Paul explained that those requiring anything beyond faith in Jesus for righteousness were perverting the gospel.
To pervert the gospel is to declare that righteousness is a combination of faith in Jesus plus adhering to a moral standard and religious system.
The reason this is a perversion of the gospel is that it ruins the gospel.
It dilutes the gospel.
It waters down the gospel.
What is the gospel?
In the gospel message, we learn that we are all sinful, all unrighteous, and that no matter how “good” we may appear to be or how many “good” works we do, we are still unrighteous.
No matter how moral we appear to be or how religious we may be, we are still unrighteous.
A person cannot behave themselves into righteousness.
If we could, then we do not need Jesus.
His life, blood, and death was a waste.
There was only one Righteous One...totally pure, totally clean...sinless, and that was Jesus.
At the cross, Jesus took all our unrighteousness upon himself...all of it.
When we place our faith in Jesus, God gives us the gift of righteousness (Romans 5:17).
God declares us to be righteous (Romans 3:21-24).
If righteousness could be earned by what we do, then Jesus' death was in vain (Galatians 2:21).
So to add any conditions for righteousness...to combine faith in Jesus with following a moral standard or religious system is to pervert the gospel.
It is to say Jesus’ death for our sins was not enough.
It is to say Jesus' blood was not enough.
It is to say Jesus' cross was not enough.
And that is a perversion of the gospel.