This week’s parshah begins with Yaakov Avinu on his deathbed. He called for and requested of Yosef not to bury him in Mitzrayim, but rather in Eretz Yisrael. Although Yosef agreed to fulfill this request, Yaakov asked him to swear that he would keep his word, which he did.
The Panim Yafos, authored by the Hafla’ah, addresses the validity of Yosef’s oath. After all, Yaakov is Yosef’s father, and as such the mitzvah of kibud av demands that Yosef heed his requests. The halacha is that when one swears to perform a mitzvah, the oath is not valid. This is because he is already obligated to perform the mitzvah. Therefore, the oath does not require him to perform a voluntary action.
The Gemara in Nedarim 8a, however, says that one may take an oath stating that he will perform a mitzvah, for it will ensure that he will not be lax in performing it. If one knows that non-performance of the mitzvah will induce an additional punishment for not keeping his oath, he will be more frivolous about keeping the mitzvah.
The Gemara quotes a pasuk in Tehillim as the source for the halacha that one may swear that he will perform a mitzvah. Asks the Panim Yafos: Why didn’t the Gemara cite the pasuk of Yosef swearing that he would bury his father in Eretz Yisrael, which he was already obligated to perform by means of the mitzvah of kibud av?
According to the Shvus Yaakov (siman 168), this question does not begin. He understands that the mitzvah of kibud av does not require that one heed his father’s request after the latter passes from this world. The mitzvah would only apply if one’s father left money and instructed his son what to do with the money after his passing. In fact, the Shvus Yaakov cites this pasuk as a source for this halacha. He asks: Why did Yaakov have to make Yosef swear that he would do this? Why was the mitzvah to listen to his command not sufficient? His answer: we see from this that there is no obligation to listen. Thus, Yaakov had Yosef swear that he would bury him in Eretz Yisrael.
The Maharsham argues with the Shvus Yaakov on this matter and refers to the Ramban here in Parshas Vayechi, who states clearly that Yaakov had no doubt that his son Yosef would observe his command. Yaakov only had Yosef swear so that Pharaoh would allow him to go to Eretz Yisrael. Yaakov knew that Pharaoh would not allow Yosef to leave Mitzrayim so easily. Therefore, he wanted Yosef to swear – so that Pharaoh would allow him to not break an oath.
It is a machlokes whether the mitzvah of kibud av requires one to heed a command from parents after they are no longer alive. Those who say that there is no obligation explain that it was for that reason that Yaakov had Yosef swear. Others who hold a contrary opinion explain that this oath was in addition to the obligation to heed the command.
The Panim Yafos answers his original question as follows: The Gemara in Nedarim 8a says that the reason why an oath that one takes to uphold a mitzvah should not be valid is because we already took an oath to uphold the mitzvos at Har Sinai. Since we already swore to keep the mitzvos, taking another oath to do so is superfluous. This is similar to swearing the same oath twice not to eat a certain food. The term the Gemara uses is “mushba v’omed” – we have already sworn to do this; thus the new oath should not take effect. The Gemara concludes that the oath does in fact take effect because it will enhance our performance of the mitzvah.