Prior to the Jewish rejection and crucifixion of Christ, a Jew merely referred to a Hebrew, generally of the tribe of Judah, attached to the Kingdom of Judea. Since then, however, it also implies the rejection of Christ and the applauding of the crucifixion, since this is what is taught in their central sacred text, the Talmud, which is merely the codification of the teachings of the rabbis since the Jews rejected and sought Christ’s crucifixion. This is why a person of Jewish ancestry who accepts Christ isn’t any longer referred to as a Jew. It’s why John wasn’t referring to Matthew, James, or Peter (for example) when he said “for fear of the Jews,” even though these folks were of Jewish ancestry. They, like most of the disciples, and all of the Apostles, in the Gospels, were of Jewish ancestry, but no longer Jews, since they didn't reject Christ, nor did they applaud the seeking and carrying out of his crucifixion. Those became, since the dawn of Christ's ministry, central elements of being Jewish.
