God overrules for good the activities of those who teach false doctrine.
In the days of the Apostles we see those activities being overruled to the production of some of our foundational New Testament documents.
Galatians is the prime example.
The heresy it combats is in its essence widespread and because of that the letter is not less necessary now that it was 2000 years agao.
It gives us a very clear answer to that most vital of questions: How as sinners can we come to be right with the God against whom we have sinned?
Nor does it leave off before it has answered the related and no less important questions: How have become right with God are to to progress in our Christian lives?