I received an email asking what is the origin of the name Jew. Here is my response.
When the Israelites broke into two kingdoms, the northern kingdom was called Israel, after the ancestor Jacob, who was also called Israel because he wrestled with men and even with God. He was not afraid to question (wrestle) with what God said, or what some people thought God said. Ten tribes joined this kingdom.
The southern kingdom was comprised of two tribes, but the largest by far was the tribe of Judah. As a result, people thought of the area as the area of Judah, and hence the name of the area became Judah and all the people, in the nation were called Judeans. (Like America and Americans.)
Later when the northern ten tribes were defeated in 722 BCE, sent into exile, and disappeared, although many of them escaped to Judah, all of the people living in this area continued to be called Judeans. (Like an Englishman becoming a citizen of America is called an American.)
Soon, the word was shortened to Jew. However, the Hebrew for Jews is Yehudim, which is Judean. How did the Y become a J? Sometime back, when Hebrew words were transliterated into English and other languages, the practice was to transliterate the Hebrew yud as a J. Thus Yerushalayim became Jerusalem, Yeshu became Jesus, Yehoshua became Joshua. Luckily yisrael did not become Jesroel, but Israel.
The word Yehudi is used in the Book of Esther, and scholars are unsure whether it means Judean there or Jew.
By the time of Paul, about whom you ask, the name came to be used for Jew, meaning a person who believed in the Jewish religion. It no longer had the nationalistic meaning for most people.
By the way, Paul according many but not all scholars did not try to convert non-Jews to Christianity, for the faith did not exist at that time, because the early Christians were Jews, he wanted to convert them to Judaism. When he saw that many non-Jews liked Jewish teachings but did not want to become circumcised, he taught that one can become a good Jew as long as he or she had faith in Jesus. He invented this idea of “faith” that did not exist previously in Judaism. Faith is the acceptance as true that which one’s senses, science, and reason say is untrue. Many Jews, in fact most Jews, bought into the Pauline notion and think that they have to have faith. It is a rare Shabbat that a rabbi does not stress that we must have faith. This bothers me very much.
Similarly, in the fourth century, Augustine invented another concept that is not Jewish “original sin.” This is the idea that people today, despite being good, are punished because Adam and Eve ate a fruit from a tree called “The tree of Good and Evil.” Even famous rabbis accepted the Augustinian notion. This also bothers me.