Remember that Jesus came to the Jews first. He preached to Jews, practiced Jewish customs, and prophesied what would happen to Jews who didn't repent. When it came to the Gentiles, he later recruited Paul to be his mouthpiece. The other disciples also interacted with Gentiles but not on the same scale. Before Paul, the disciples didn't know that the Word was for all mankind instead of just for Jews. When the Holy Spirit sent Peter to Cornelius, Peter was amazed that the Word was for Gentiles, too. He'd just spent 3 years with Jesus and didn't know that as everything Jesus was teaching was aimed at the Jews. The other Christians were shocked to hear that Peter had baptized Gentiles.
After the Roman invasion, the Jewish way of life was gone forever. It was the Gentiles who spread the Word from that point on.
