Many scholars throughout the ages addressed the question of how Yaakov allowed himself to marry two sisters (Rachel and Leah), in light of the Talmudic tradition that the patriarchs followed Torah law, even though the Torah had not yet been given. The most famous answer, perhaps, is the theory advanced by the Ramban, in his commentary to Parashat Toledot (26:5), that the patriarchs observed the Torah’s commands only in Eretz Yisrael. He writes, “The mitzvot are the law of the God of the Land,” and they therefore must be followed only in God’s Land – Eretz Yisrael. Thus, Yaakov was permitted to violate the Torah’s marriage restrictions while he lived in Charan, outside the Land of Israel.
Rav Yaakov Kaminetzky, in his Emet Le-Yaakov, offers a surprisingly simple explanation for why Yaakov allowed himself to marry Rachel after marrying her sister. Yaakov not only desired to marry Rachel, but also made a solemn promise to her that he would marry her, as the Ramban himself notes in his commentary later in Sefer Bereishit (48:7).
If we assume that Yaakov followed Torah law even in Charan, then after Lavan deceived Yaakov and brought him Leah instead of Rachel, Yaakov faced a dilemma. He had made a promise to Rachel that he would marry her, but this would require violating the prohibition against marrying sisters. He would either have to violate his vow to Rachel or his commitment to Torah law. In truth, however, this was no dilemma at all.
Yaakov was not required to obey Torah law before it was given, and he committed himself to it voluntarily. Certainly, his voluntary religious standards should not get in the way of his fulfilling his formal obligations to another person. The strict moral obligation of keeping one’s word undoubtedly takes precedence over voluntary measures of piety, and Yaakov therefore married Rachel even though he had already married her sister.
Rav Yaakov Kaminetzky asserts that even the Ramban followed this line of reasoning. The Ramban’s discussion, according to Rav Yaakov, focuses on a different question, of why Providence arranged the events in such a way that Yaakov would be forced to violate the Torah’s marital laws. The Ramban answers that the patriarchs committed themselves to these laws only in Eretz Yisrael, and thus in truth Yaakov did not violate even his voluntary commitment to Torah law by marrying Rachel. But it is clear and obvious, Rav Yaakov claims, that Yaakov would not have broken his promise to Rachel for the purpose of abiding by self-imposed religious measures which were not strictly required.