4 Have you suffered so much for nothing, if it really was for nothing? -Galatians 3:4 BSB
The Galatian church, just like every other true church, went through difficulties and challenges as followers of Jesus Christ. Paul was concerned that some of them got confused with very convincing arguments about going back to the Law and keeping it for righteousness. According to Galatians 4:17, there were false believers, Judaizers, who had deep desires to have the Galatian church follow them and abandon Paul and his companions.
Paul was hoping that they didn’t run the race in vain, thus this letter of correction to get them back to sound doctrine.
A person can claim to follow Jesus and start on the right track, but then encounter a stumbling block down the line that will take them down the wrong path through deception.