Why were the Judaizers and the Orthodox Jews both wrong about salvation?

Both were wrong because they insisted that keeping the Law and practicing circumcision were necessary for salvation. Whether they rejected Jesus or embraced Him as Messiah, they added legal requirements to the gospel, claiming Paul’s message alone could not save. That made their teaching contrary to Paul’s message of salvation.

Les explains that the Judaizers were the Jewish element from Jerusalem, whether Orthodox Jews who still rejected Jesus of Nazareth or Judaizers who had embraced Christ as the Messiah. He says it makes 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. These Judaizers came into the little congregations Paul had planted through his sweat, blood, and tears, telling them they could not be saved by Paul’s message alone. This fits the broader warning that many theologians, pastors, and preachers ignore Paul’s writings, yet this is where we must be if we are going to know the truth of God for this age of grace.

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.