WHO IS A JEW?
The Jewish people is a religio-nation, meaning that it is a people that consists of two coexistent and intertwined components: Ethnicity and Religion. Consequently, the Jewish people constitutes both an ethnic nation and a faith community. However, the former component of Jewish peoplehood is involuntary and immutable, while the latter component thereof is voluntary and mutable.
It is a unique collective, in that it is the only religio-nation born in Antiquity that, despite being dispersed throughout much of the World for the greater part of its history, continues to exist Today.
Ethnically, the Jewish people is comprised of:
(1) the descendants of the eponymous Hebrew tribe of Judah, together with the descendants of the Hebrew tribes of Levi and Benjamin, the latter of which is the product of intermarriage between the surviving male members of the Hebrew tribe of Benjamin and female members of the Hebrew tribes of Manasseh (from the City of Jabesh-Gilead) and Ephraim (from the City of Shiloh) (see Judges 21:1-23); and
(2) those Gentiles who have converted to Judaism throughout History.
Although not an ethnic Jew, a Gentile nonetheless becomes part of the Jewish people by joining the latter’s faith community (i.e., acceptance of the God of Israel and the Truth of His Torah) and by simultaneously self-identifying as a Jew. This two-component formula for becoming part of the Jewish people was first uttered by Ruth, the Moabite ancestress of biblical Israel’s King David (and of the future Messiah):
“And [widowed] Ruth said [to her widowed mother-in-law Naomi], ‘Do not urge me to leave you, to turn back from following after you; for, where you go, I will go; and where you lodge, I will lodge; your people are my people, and your God is my God.’” (Ruth 1:16)
The ethnic-religious duality of Jewish identity means -- uniquely -- that a Jew who later repudiates Judaism (or even the Existence of God) nonetheless continues to be part of the Jewish people, as such an apostate nonetheless remains an ethnic Jew. This duality distinguishes Jews from Christians, Muslims and adherents of other religions, precisely because the latter lack a unique ethnic component (i.e., the latter are merely religions, not religio-nations). So, while the Jewish apostate may continue to be identified (and to self-identify) as a Jew, the Christian apostate and the Muslim apostate can no longer be identified (or self-identify), respectively, as Christian and Muslim.
Although intermarriage between members of the Hebrew tribes and Gentiles is prohibited by the Torah (see Deuteronomy 7:3-4) and, consequently, also by normative Judaism, when such a union does happen a question arises as to whether the offspring thereof is to be recognized as a Jew. In such a case, the Orthodox branch of Judaism (which, until several hundred years ago, constituted the entirety of Judaism) has traditionally recognized as a Jew the child of a Jewish mother (i.e., matrilineal descent), but not the child of a Jewish father (i.e., patrilineal descent). However, I disagree with this formulation, as the child of a Jewish father in such a union is as much a (partial) ethnic Jew as is the child of a Jewish mother. Rather, I believe that the child of such a union ought to be recognized as a Jew if and when such a child self-identifies as a Jew, but not otherwise. This means that, in the case of intermarriage, the Jewishness of a child of a Jewish mother ought not be automatically accepted; and that the Jewishness of a child of a Jewish father ought not be automatically rejected. While such a formulation is considerably more complex than a bright-line rule which accepts matrilineal descent and rejects patrilineal descent, it properly includes those people as Jews who self-identify as such (even if their Jewish parent is male), and it properly excludes those people as Jews who do not (even if their Jewish parent is female).