Were Rachel and Leah Jewish?
Taste of Mishna
The first Mishna in the third chapter of tractate Yevamos deals with a case where two brothers, Reuvain and Shimon, married two sisters, Rachel and Leah. Tragically both brothers pass away childless, survived only by another two brothers, Levi and Yehuda. The Mishna says they should not do Yibum. If they go ahead and are Miyabaim Rachel and Leah, there is a dispute between Bais Shammay and Bais Hillel if they may stay married. The reason for the opinion that says they must separate is that a man may not marry two sisters and since Rachel and Leah were both waiting to marry each of the surviving brothers there is a problem called “achos zekukaso”. This means that a man may not marry the sister of a woman that is waiting to have Yibum done to her by him because it is like he is considered to be married to her already, Rabbinically. Therefore in our case neither woman may stay married because each of them is an “achos zekukaso”.
Taste of Halacha
The Rambam says the Halacha is like the opinion that they may stay married to Rachel and Leah. Why? The Bach explains the Rambam only permits them to stay married in a situation where Reuvain and Shimon died one after the other and we do not know which of them died first. Therefore each brother may stay married because in this case once one brother marries the wife of the one who died second he removes her connection to the other brother so she is no longer waiting to marry him so the second brother’s marriage is justified as Yibum without her being an “achos zekukaso”. This is so even though we do not know for sure who was the one to marry the first and who the second, because each of them could say, “I married the wife of the one who died first after my brother removed the connection of the one who died second!” And the Rabbis do not enforce their decree of “achos zekukaso”, in a case of doubt, ex post facto / “bedieved“.
Taste of Parasha
The Gemarah in Yoma, 28B, teaches that Avraham Avinu kept all the Mitzvos of the Torah and taught them to Yitzchak who taught them to Yaakov. If so, how is it that we find Yaakov Avinu marrying two sisters in this week’s Parasha? The Maharsha has two answers; first of all, Rachel and Leah were born to non Jews so they had to go through a conversion. A convert who converts is like a new born child so they were not related to each other! Another answer is that Yaakov had already legally consecrated Rachel to him through his work for Lavan for seven years. Then unbeknownst to him he became married to Leah through Lavan’s trick. Therefore he was not obligated to separate from them because the Torah was not actually given yet so it is like a Rabbinic decree! And the Rabbis do not enforce their decree, ex post facto / “bedieved“!