What did the Judaizers tell the Gentile converts they had to do?
The Judaizers from Jerusalem told Gentile converts they had to keep the Law of Moses, be circumcised, and do the things required by the Law. They undermined the Gospel by insisting these works were necessary, and the Galatians were beginning to fall to that teaching.
Les explains that once Gentile converts began coming under His Gospel, Judaizers from Jerusalem started to undermine it. They kept trying to convince these Gentiles that they had to keep the Law of Moses, be circumcised, and do those things. The Galatians were falling to that teaching, which is why Paul made a stringent statement, as reviewed in Galatians chapter 1.