Even those far removed from Jewish learning know that it is the mother who determines the Jewish status of a baby. Why this is so is not clearly spelled out. The simplest and most obvious reason would seem to be the fact that while we always know who the mother is, the identity of the father is less certain. The Talmudic assertion that "the majority of relations a woman has is with her husband" (Sotah 27a) is just that--a claim about the majority. However, a minority are not.
who is a Jew
The assimilation and subsequent loss of Jews has been a problem since the beginning of Jewish history. Many of us were taught--in kindergarten, no less--how Abraham and Sarah converted many to Judaism. This is the midrashic explanation of the verse we will read next week, “and the nefesh, souls they made in Charan” (the simple explanation is that nefesh refers to the wealth they had acquired). Yet these anonymous people or their children must have assimilated, as we never hear from them again.