What did both the unbelieving Orthodox Jews and the Judaizers agree you had to do to be saved?
Both groups agreed that salvation required keeping the Law and practicing circumcision. They insisted that without these works, a person could not be saved, and they rejected the idea that Paul's message alone was sufficient for salvation. This was the common ground between the unbelieving Orthodox Jews and the Judaizers.
Les explains that the Judaizers, the Jewish element from Jerusalem, came into the little congregations Paul had planted. Whether they were Orthodox Jews who still rejected Jesus of Nazareth or Judaizers who had embraced Christ as the Messiah, it made little difference, because both were hung up on the fact that you had to keep the Law and practice circumcision, or you could not be saved. They told Paul that you cannot be saved by his message alone; you cannot be saved like he says.