What makes someone Jewish by blood?
A person is Jewish by blood because he descends from the promised covenant line of Abraham, Isaac, and Jacob. Specifically, being from the twelve tribes of Israel makes him a Jew by blood, not merely by religion. This lineage, not religious practice alone, defines Jewish blood identity.
Les explains that the Jewish people began when God called Abraham out of an idolatrous civilization, as Joshua 24:2 records that Terah, Abraham's father, and his forefathers served other gods. From that race of humanity, God took one man, Abraham, and this became the beginning of the nation of Israel, commonly called the Jew. When asked what makes a Jew a Jew—religion or blood—the answer is both. Yet first and foremost, a Jew is one who comes out of the promised covenant line of Abraham, Isaac, and Jacob. If he has come out of the twelve tribes, that makes him a Jew by blood.