A perversion.

Galatians 1:7 NKJV
“…which is not another; but there are some who trouble you and want to pervert the gospel of Christ”

Galatians 1:6b-7 TPT
“…I’m frankly astounded that you now embrace a distorted gospel! ⁷ That is a fake “gospel” that is simply not true. There is only one gospel—the gospel of the Messiah! Yet you have allowed those who mingle law with grace to confuse you with lies.”.

Galatians 1:7 AMPC
“Not that there is [or could be] any other [genuine Gospel], but there are [obviously] some who are troubling and disturbing and bewildering you [with a different kind of teaching which they offer as a gospel] and want to pervert and distort the Gospel of Christ (the Messiah) [into something which it absolutely is not].”

The problem that Paul was addressing with the believers in Galatia was that they were falling for a perverted gospel (NKJV) or a fake gospel of lies (TPT). The word “gospel” literally means good news and it is the good news of what Jesus has done for us and freely offers us. News is something that happened in the past; it is not prophecy or foretelling of the future. The gospel is good news about what has happened not what should happen. It’s good news about what Jesus has done for us, not news about what we should do for Him. It’s good news about what Jesus freely offers us; it’s not about what He expects or demands of us. So, how would you pervert or distort the gospel? Simply by adding to it. This is what Paul was dealing with in his letter to the Galatians! Legalistic Jews were coming to the believers and preaching a false message of lies to them; they were preaching a perverted and distorted gospel. And sadly, the Galatians seemed to be falling for it. Since these legalists were perverting the gospel you could say that they were perverts. 

The gospel was being perverted or changed by saying that in addition to faith in Christ for salvation (1) it is necessary to observe special days (Sabbaths), months, seasons, feasts and years (Galatians 4:10); (2) and circumcision was still essential for salvation (Galatians 4:10, compare with The Living Bible). The perverted gospel also proclaimed the non-good news that (3) part of our righteousness comes through observing the Law (Galatians 5:4) and (4) that righteousness can be obtained by the strength and ability of their own flesh (effort) (Galatians 3:3).

The bottom line is that it’s all Jesus or nothing. Jesus + nothing = salvation (including a relationship with God) while Jesus + anything (any effort to earn or deserve) = nothing.

“The just shall live by faith.” (Romans 1:17) We don’t live by what we can do for God but by faith in what He has done for us! Today we still try to add things to the Gospel. We tell people that they can be saved by grace through faith, but they still need to… and then we add many things which have the appearance of good and right but in essence are mere distractions from Jesus. Whenever something or someone takes the focus of Jesus, it’s a perversion. Adding to the pure message of the Good News of God’s unconditional love and grace makes you a pervert.

Perverting the Gospel renders the Gospel powerless in our lives. You cannot dilute the good news of His grace and be left with the power to save. The power to save is in the purity of the Gospel. Only the pure Gospel will bring purely powerful fruit in our lives.