This was the apostle Paul's frustration with the Galatians. People came in after Paul and give these young Christians other beliefs (namely that they had to convert to Judaism before they could really be followers of Jesus) that lead them away from Jesus. This is what Paul writes:
6 I am astonished that you are so quickly deserting the one who called you by the grace of Christ to follow a different gospel, 7 which is not really another one. To be sure, there are certain people who are troubling you and want to distort the gospel about Christ. (Galatians 1:6-8; ISV)Let this be a warning to us. We have to be discerning about the "truths" and the "beliefs" we allow into our lives, because some will lead us very far away from Jesus.