Christianity are not concerned with a question 'who is a Jew'.
I just want to refute this. Christianity is significantly concerned with the origins of Jesus, and in fact his Genealogy is the very first thing
the New Testament opens up with. This is because Christians believe Jesus was the Jewish Messiah and this figure must be strongly connected to King David through the genealogies and according to the Tanakh must be born in the ancestral home of King David.
Yes he was Jewish because he practiced Judaism, but he was also ethnically Jewish because he was of the Tribe of Judah and descended from King David(on his mother's side, and also legally on his adoptive father's side). This is extremely important to Christianity because it is a fundamental tenant of the faith. You can't believe in Christianity without taking an interest in the origins of Jesus and in his Jewishness, because Christians believe Jesus was the Messiah.
Also read this:https://biblehub.com/drb/romans/2.htm
The question of "Who is a Jew?" is significantly explored in this entire chapter of the book of Romans, as well as the entire Letter to the Hebrews(/Jews), as well as John's famous (and controversial verses) about "fake Jews" + "synagogue of Satan" from Revelations. So you are quite wrong. Paul and John were both Jews.
The book of Acts also briefly brings up this topic when it covers how the disciples decided to now also preach to non-jews.
Perhaps you need to ponder as to why you are concerned about that, when your own religion is not?
Except it is. The Authors of the New Testament were all Jews and bring up the concept of "What is a Jew?" quite frequently as I just pointed out. The first thing that is explicitly stated is Jesus is the Jewish
Messiah, is descended from David
, and is the King Of The Jews
as well as the Lion of the Tribe Of Judah
You may not agree with the Second Temple Period view that Jews are the ethnic descendants of the Tribe of Judah(+Benjamin) and that Jews which do not commit the Blood Sacrifice are "fake Jews(I.e Heretics)", but deep down inside I know you know your Religion significantly changed with the writing of the Talmud.
Your position is the position of Talmudic Judaism, however Second Temple Period Judaism had different views on what makes a person Jewish. I'm glad you've accepted this fact, since it is moronic to assume your Religion "hasn't changed one iota in 2000 years". No I don't need to go to your Rabbinic Authorities to ask them what a Jew is since we both know they'll give me the Talmudic view that Jews practice Talmudic Judaism....
But we both know to Second Temple Period Jews, you would be considered a heretic to the religion and not Jewish at all since Judaism to them requires a large amount of Animal sacrifice for your sins to take place on Mount Moriah. That's Second Temple Period Judaism
. You don't do that so to Second Temple Period Jews you would not be a Jew at all.
Also the Temple Genealogy records existed in the time of Jesus, so Jews knew their "tribal affiliations" and could scientifically prove from their family record they were descended from Judah and/or Benjamin. Herod The Great possibly destroyed all these records so no Jew could prove which tribe they descended from, the Sicarii later totally destroyed the "Hall Of Records" in Jerusalem to wipe out their financial debts in the first Roman-Jewish conflict, the Temple(with its copy of the major records) was burnt to the ground and the Romans destroyed everything else in the entire country. Nothing was left. Either way you look at it the Jews entire ancient administrative, financial and genealogical records were totally wiped out.
This is the main reason you modern Jews place far less emphasis on Ethnicity since no modern Jew can prove his Genealogical tribal affiliation, this inspite of the fact the Messiah, according to your belief system, will be an Ethnic Jew fully directly descended from the line of King David
and that will require direct evidence he is descended from David. Of which there will be zip.
According to your belief system.... The Messiah Must Be An Ethnic Jew Of The Davidic Line