Only with Paul did YHvH extend the good news to gentiles.
These two statements contradict each other. Even IF everthing except the Pauline Epistles were written "by Jews and for Jews," the reality is that Saint Paul's letters show an incredible focus on converting Gentiles to Christianity.
And then there is the question of the Gospel of Saint Luke and Acts. Saint Luke was for certain converted by Paul and many believe that he was probably a Gentile.
But there is no scriptural evidence that he was not a Jew.Paul converted Luke to be a follower of the Messiah.
b'SHEM Yah'shua