The Galatians had been taught by Paul himself, so I don’t think they would’ve been taken in by someone preaching something that sounded nothing like the true gospel. If these other preachers in Galatia had made it really obvious that they were blatantly opposed to the basics of the Christian faith, I doubt the Galatians would’ve listened. And I doubt those preachers were deliberately trying to lead the Galatians astray.
In most films, it’s really who obvious who are the goodies and who are the baddies; the baddies clearly have evil intentions. And the media often portrays real life in a similar way. But real life isn’t usually like that. In general, everyone believes they’re doing the right thing, and I think it’s probably fair to assume these preachers in Galatia believed they were preaching the truth. I expect they thought they were preaching a version of Christianity that was more honouring to God than Paul’s message of totally free grace, but a sincere desire for God-honouring truth in preaching is not enough to redeem a sermon that in fact distorts the gospel of Christ.
A gospel contrary to the one we preached
Later on in the letter we’ll see what the difference was between the gospel Paul preached and this other gospel that was being preached in Galatia, but basically, these preachers were not denying that the Galatians needed to trust in Christ for their salvation, they were just adding that there was something else they should do as well to make themselves acceptable to God.
As I wrote that last sentence, I was imagining how I would react if I was listening to someone else say it, and I think, if I didn’t already know what it was that the Galatians had been taught they should do to make themselves more acceptable to God, my ears would’ve pricked up at this point.
“There’s something I can do to make God extra pleased with me? What is it?” Even though I know in theory that God is already as pleased with me as he’ll ever be, on the basis of Christ’s righteousness that I’ve been given as a free gift, I still find myself attracted to the idea of doing some good deed to impress God. I need constantly reminding that there is no deed I can do to make myself more righteous. I’m justified by grace alone, though faith alone, in Christ alone, to the glory of God alone.
If anyone preaches anything different to that, or if they add anything to it, they’re distorting the gospel of Christ.
For example, if someone says “yes, you’re saved by grace alone through faith alone in Christ alone, but to make sure God is still pleased with you today, you need to do (this) for him, or, to earn extra favour from him this week, you could serve him by doing (this)…” they’re distorting the gospel.
If we could ever earn anything from God, then it wouldn’t be grace, it would be our wages, and we would deserve some glory, but the gospel is we receive grace from God and he gets all the glory.
That’s why Paul describes the gospel that the Galatians were turning to as not only “a different gospel”, but “a gospel contrary to the one we preached”. Any suggestion that we can do any work to make ourselves righteous, or earn blessing from God, is the opposite of the true gospel.