Jewishness and the Book of Ruth
Preface: In this article I use the term “nation” synonymously with “people”, as this is its oldest sense. I am most emphatically not referring to the modern concept of “nation-states.”
The Jewish nation or Jewish people is an entity larger than a tribe which has existed since antiquity independently of its particular rulers, who were often foreign (Roman, Babylonian, Persian, etc.). Jews comprise the tribes of people who claim descent from the Biblical Israel and lived, in ancient times, in the South of present-day Palestine/Israel, as opposed to the northern nation of Samaritans. Most of our individual tribal identities are lost, though the tribe of Levi has maintained its individual identity for liturgical purposes, as has the particular subgroup of Kohenim (Priests) within the tribe of Levi.
On Shavuot, an ancient pilgrimage/harvest festival that has just passed at the time of this writing, Jews traditionally read the Book of Ruth, which is about a woman from Moab (present-day Jordan) who, during the time of the Judges, went to the land of Israel, joining the people (nation) of Israel and becoming an ancestor of the Jews' second king, David.
Along with the many religious messages that can be gleaned from this, I also like to think it is saying something very important about what constitutes membership in the Jewish people. Whether or not Ruth was a true story (and I doubt it was), it was a part of Jewish culture then and it is part of Jewish culture now; it was used to teach our cultural attitudes and beliefs to our children and to the people who, like Ruth in the story, chose to join the Jewish people.
There are many people who argue that Jews are nothing more than a religion; that the Jews may have been a people in ancient times, but are not anymore. They argue that the lineage of the Jewish people is largely either gone or so mixed with the other peoples of the world as to be irrelevant. This demonstrates either ignorance or omission of the opinions of actual ancient Jews as transmitted through stories such as that of Ruth.
Many will claim, contrary to academic consensus and without evidence that would overturn such consensus, that Ashkenazi Jews are Khazars. They might point to genetic studies which show that many Ashkenazi Jews are descended from European women and Jewish men, therefore “proving” that Ashkenazim aren't Jews. They may even argue that Palestinians are the real descendants of the Jews, even if they are Muslims, Christians, or members of other religions, while holding Palestinians to a much lower standard for having such descent recognized than actual Jews.
Jews, however, have always seen ourselves as a people, from ancient times to modern times. And the Book of Ruth makes it clear that “the Jewish people” are not a strict genetic lineage, and nor were we during the time of Ancient Judaism. As a matter of fact, in the story, Ruth's descendant goes on to be King of Israel, defeating someone who seemingly was not descended from a convert, Saul.
As a result, even if it were true that there were Khazar converts among us, it literally wouldn't make the least bit of difference to what constitutes Jewishness. This was a Jewish truth in ancient Judah, it remained a Jewish truth in the Diaspora, and it remains a Jewish truth today: Jew has always clearly meant a member of a group sharing a religion, culture, language, etc., including the new people who join us. Thus in any meaningful sense, today's Jews are the Jews that have existed since ancient times.
None of us popped out of nowhere. Culture is transmitted from one person to the next: parent to child, child to parent, community to child, child to community, rabbi to child, child to rabbi, community to convert, convert to community, rabbi to convert, convert to rabbi, convert to child, child to convert. Culture and society are the only senses in which any nations exist.
I don't care why you're doing it: it's never ok to deny the continuity between ancient and modern Jews, or ancient and modern Judaism. It's flat-out wrong, demonstrates a lack of respect for the actual traditions and beliefs of our ancestors, the ancient Jews, and is usually done to legitimize erasure or dismissal of Jewish history. And if you need to make such arguments to justify anti-Zionism, which you shouldn't, then maybe you, specifically, are more than just an anti-Zionist.