Early in the book of Galatians, Paul, the Apostle, pointed to a problem for the Galatian believers. What Paul identified was that some of the Galatian Christians wanted to impose Judaic customs on other believers. Some Galatians believed that Mosaic (Jewish) customs were essential to salvation while others claimed they were essential for spiritual growth. In Galatians, we see Paul strongly arguing against these ideas and teachings.
Paul starts his letter to the Galatians by defending the Gospel and his Apostleship. Paul reminds them that his salvation and growth as a Christian was independent of men and even separate from the Apostles in Jerusalem. Paul comes out against the teaching that Diaspora believers must become like Judaics to be right with God.
Paul makes it clear to the Galatians that the only true children of Abraham were believers in Jesus Christ whether they be Judeans or Diaspora believers.