Comentário sobre Gênesis 25:33

SWEAR TO ME THIS DAY. When Esau said, “What is this birthright to me? I do not desire it,” Jacob said to him, “Swear to me that you will not desire it, nor will you inherit it forever.” Thereupon he swore to him, and following that he sold it to him, and Jacob gave him the purchase price⁶⁴That is, the money. This is in accordance with the opinion stated above. Although Ramban does not agree with it, he nevertheless mentions it as an alternate interpretation of the verse. or the pottage he desired.
It is possible that Esau said, “What is this birthright to me? It is sold to you,” and Jacob said, “Swear to me that you will never complain about the sale.” And when Scripture says that first he swore to him and then he sold it to him, its intent is as if it said that he sold it to him first and then swore to him.

השבעה לי, seeing that the purchase under discussion was something abstract, the oath would replace the act of physically taking possession of the object purchased and moving it.

ויאמר השעבה לי. He said: "swear it to me on an oath." The reason that Jacob requested an oath from Esau was because the whole institution of the birthright contains many intangibles, such as the honour and dignity conferred on the firstborn. Jacob was particularly interested in the privilege of performing duties in the Temple, something which was the duty of the firstborn at that time. We are conversant with the rule that a person cannot transfer the right to intangibles either by sale or by gift (Maimonides Hilchot Mechirah chapter 22). This is why Jacob insisted on making such acquisition by means of an oath. Yoreh Deah 239 rules that both tangibles and intangibles may be acquired by means of an oath.

ויאמר השבעה לי, he was afraid that Esau would have second thoughts after having eaten.

וימכור את בכורתו, in exchange for money. After this Yaakov gave Esau the reddish looking dish of lentils he had cooked, as is customary among people sealing a bargain.

השבעה לי כיום “swear it to me as of this day. Yaakov requested an oath that Esau would not change his mind about this deal at some time in the future. This was the only way that the sale would have meaning for him. He did so because the Talmud teaches that if someone announces: “I will sell you whatever I will inherit from my father,” such a statement is legally meaningless. (Baba Metzia 16).

וימכור את בכורתו, in accordance with the price they had mutually agreed upon. The Torah did not bother to spell out the exact sum.

Jacob used the words "swear it to me." Actually the oath is not sufficient to acquire an intangible which does not even exist yet such as becoming heir to one's father if the latter dies before the heir. The reason is that the purchaser cannot truly have convinced himself that he will ever obtain what he has purchased (Baba Metzia 16). If, however, the purchaser was absolutely certain in his mind, the object has indeed been acquired and the oath is quite irrelevant. This is why Jacob had to add the words כיום, as I have explained already. In the meantime I have found a book of the Rivash in which he writes as follows in the course of item number 328. "You have written that you have seen that the son of the Rosh wrote in the name of his father that if someone tried to acquire a "future" by means of an oath such an acquisition is legally valid. He proves the thesis from the sale of the birthright from Esau to Jacob and the fact that the latter insisted on an oath. Since we have neither the signature of the Rosh or his son Rabbi Yaakov to confirm such a theory, it is not admissible to place such theories in the mouths of great men [in order to lend them weight Ed.] seeing that the theory has absolutely no merit. The "so-called" proof from our story is no proof at all seeing that all this occurred before the Torah was given to the Jewish people. It is quite possible that in those days people did not distinguish between selling "futures" and selling "actuals." The oath then would merely have served to reinforce the sale, to protect oneself against the seller changing his mind at a later date. Esau was, after all, a man of violence." Thus far the Rivash. This is exactly in agreement with what we have written, the only difference being that the Rivash did not see fit to provide a reason why Jacob insisted on an oath.

The reason Jacob said: "swear an oath on it to me," instead of merely "swear an oath on it," is so that it would be understood that the sale was for the benefit of Jacob (not for someone else). The oath had to be acceptable to Jacob else Esau could have annulled it in his heart. The essential element of an oath is the heart, i.e. what a person has in mind at the time of the oath (compare Rabbi Akiva in Torat Kohanim 12). Rabbi Akiva insists that at the time an oath is sworn the person undertaking it must have no reservations about the declaration he makes on oath. When Jacob said "swear it to me," he meant: "make your oath correspond to my will."

Another reason Jacob was careful to add the word לי "to me," was that only he was able to acquire the birthright. Inasmuch as the benefits of the birthright include such intangibles as the duty to perform sacrificial service in the sanctuary, this was something that devolved from Isaac to his son. This privilege could not be sold to anyone who was not a son of Isaac. The dignity of the office of the priesthood (in those days equivalent to the birthright) could also not be transferred to an outsider.

וימכור את בכרתו, He sold his birthright, etc. The Torah here had to state the validity of the sale a) because of the reasons we have explained, b) because Esau acted under some kind of duress, c) that Esau sold something for a mere fraction of its real worth. In his commentary on Choshen Mishpat item 227, the Maharik writes as follows: "if someone sold something due to pressing need even at a price significantly below its accepted market value, he cannot retract because he was aware of what he was doing and forgave the difference in value to the purchaser." In view of this ruling the fact that Esau sold the valuable birthright for a single swallow of Jacob's potage did not invalidate the sale. Esau had described his state of exhaustion as: "here I am about to die;" there is no greater emergency than a person selling something in order to save his life. We know from Job 2,4 that a person will give up all that he has for his life. Had Esau not been in such a state, Jacob could not have acquired the birthright from him. When Solomon said in Proverbs 5,22 that the wicked will be entrapped by their iniquities, he had Esau in mind. According to Bereshit Rabbah 63,14 Esau had committed a number of sins on that fateful day and this was the reason that he forfeited the birthright which was transferred to someone more deserving than he.