Jacob's marriage to Rachel and Leah, Laban's daughters, is related in this week’s Torah portion, and many commentators grapple with the question of how Jacob was permitted to marry two sisters — in view of the fact that he kept the entire Torah before it was given1, and the Torah explicitly forbids such a marriage2. A summary of a profound and scholarly explanation of the question by the Rebbe follows.

Our forefathers took upon them-selves to keep the entire Torah — even though they had not been commanded to do so — as an extra added measure of devotion to G‑d. If those Mitzvot or commandments of the Torah which they were not ordered to observe happened to conflict with precepts that they had been explicitly ordered by G‑d to observe, then they obviously did not keep the Mitzva that they were not commanded. In fact, such action constituted for them true Torah-observance; the Torah itself required that they refrain from doing an extra, added act of devotion when this was in conflict with an explicit command.

Aside from the precepts that Noah and his descendants had been specifically commanded by the Al-mighty to observe, they also took upon themselves, as a communal responsibility, additional moral laws3, which then became mandatory according to the Noahide laws and according to the Torah4. If one of these universally-accepted laws conflicted with one of the "Sinai-Mitzvot" that the Patriarchs observed as their own particular custom, here too they were not allowed to fulfill that "Sinai-Mitzva." An example of such a universally-accepted law of society was to refrain from deceit, so that even Laban "the swindler" felt compelled to try and 'explain away' and excuse his deceit of Jacob.

Jacob had promised Rachel he would marry her. Failure to keep his promise would constitute grave deceit — and would cause Rachel particularly great distress because she feared she might become the bride of Esau5. Consequently, although he was already married to Leah, Jacob was in this case not allowed to observe the future law of not marrying two sisters, but was required to fulfill his promise and marry Rachel.

There is a simple forthright teaching that each one of us can derive from the above: If a person should desire to take upon himself extra niceties of observance, he should first make sure that this is not at the expense of others. If one knows of — and is capable of helping — a person ignorant of his Judaism and gravely in need of the basic essentials of Torah-education, then he has no right to think "I'd rather use the time to elevate my own studies and observance to a superlative level." The challenging question he must answer is this: Is he so much more worthy and important than the other that he can justify adding refinements to his own Torah-study and observance at the expense of another's basic spiritual needs?6