The Torah's description of Esav's sale of his birthright to Ya'akov leaves open several questions:

1. What were the privileges and/or responsibilities associated with the birthright?

2. Did Ya'akov trick Esav in the sale of the birthright, or was the sale by mutual consent?

3. Why did Esav despise the birthright?

The Nature of the Birthright

Rashbam and Ibn Ezra suggest that the birthright of Esav had monetary value relating to the double portion that goes to the first born son in the inheritance.

אבן עזרא: והבכורה שיקח פי שניים בממון אביו.

רשב"ם: מכרה לי- מיד מכור לי חלק בכורתך הראוי לך בממון אבי בממון שאתן לך ואח"כ אתן לך המאכל לעדות ולקיום.

Ibn Ezra: The birthright was that he would take a double portion of his father's money.

Rashbam: Sell to me - Sell to me immediately the portion of your birthright that is coming to you from my father's money for the money that I will give you, and afterwards I will give you food as testimony and closure.

Thus according to Ibn Ezra and Rashbam, the sale of the birthright was a simple business transaction that gave Esav immediate use of the extra portion destined for him in the inheritance of his father's assets. Rashbam claims that Ya'akov actually purchased the birthright with money, and not with the food that he gave to Esav. The meal was, rather, the customary method of indicating the completion of an agreement.

Ramban claims that the birthright of Esav was unrelated to the double portion in the inheritance, because that provision was not in force during the time of Ya'akov and Esav. The concept of a double portion for the first born son was an innovation of the Torah law that took effect only at Sinai. Rather, Ramban suggests that the birthright related to prestige and power:

רמב"ן: ויתכן כי פי שנים בבכורה ממשפטי התורה ולא היה כן לפנים רק לנחול מעלת האב ושררתו שיהיה לו כבוד ומעלה על צעירו.

Ramban: And it is possible that the double portion of the first born was from the laws of the Torah and was not in force before. Rather, it was to inherit the position and authority of his father so that he would get greater honor and status than his younger brother.

Ibn Ezra presents the same idea in an alternative explanation:

אבן עזרא: ויש אומרים שיש לבכור לעולם מעלה על הצעיר לקום מפניו ולשרתו כבן לאב.

Ibn Ezra: And there are those who say that the first born always has status over the younger one that he rises before him and serves him as a son toward a father.

Rashi and Sforno offer an alternative explanation of the significance of the birthright of Esav. They contend that the first born bore special responsibilities relating to the divine service. This was the original intent of the Jewish tradition before that responsibility was transferred to the sons of Aharon, who became the priests[1].

רש"י: בכרתך לפי שהעבודה בבכורות אמר יעקב אין רשע זה כדאי שיקרב להקדוש ברוך הוא.

םפורנו: באופן שאתה כל כך עיף שאינך מכיר הנזיד אין ספק שלא תוכל ךהתעסק בעניני הבכורה לשרת לאל יתברך ולעשות הראוי לבכור.

Rashi: Your birthright - Because the worship was conducted by the first borns, Ya'akov said: “This evil person is not suitable to bring sacrifices to the Holy One Blessed Be He.”

Sforno: As you are so tired that you cannot even recognize the pottage, there is no doubt that you will not be able to engage in the matters of the first born, to serve God and to do that which is appropriate for the first born.

According to Rashi, Esav was not suitable for this level of religious responsibility because of his evil qualities, while Sforno claims that his nature and his other pursuits precluded Esav taking responsibility for spiritual matters.

And Esav Despised the Birthright

The commentators correspondingly differ as to why Esav despised the birthright. According to Rashi, Esav was not interested in taking responsibility for the divine service.

רש"י: הנה אנכי הולך למות - אמר עשו מה טיבה של עבודה זו. אמר לו כמה
אזהרות ועונשין ומיתות תלויין בה כאותה ששנינו אלו הן שבמתה שתיי יין
ופרועי ראש. אמר אני הולך למות על ידה אם כן מה חפץ לי בה. ויבז עשו -
העיד הכתוב על רעשו שביזה עבודתו של מקום.

Rashi: Behold I am going to die - Esav said: “What is the nature of this service?” He said to him: “There are a number of warnings, punishments, and deaths associated with it, as we have learned: ‘these are punishable with death – those drunk with wine and those with uncovered head.'”

He said: “I am going to die because of it; if so, why do I want it?”

And Esav despised - The text attests to his wickedness in that he despised the service of God.

Rashi connects Esav's rejection of the birthright with his statement that he is going to die. In Rashi's formulation, there is a cause and effect relationship between the birthright and his death – i.e. that he will die as a result of improper fulfillment of his responsibilities relating to the worship service. Rashbam and Ibn Ezra also relate Esav's rejection of the birthright with his statement that he is going to die, but in the opposite manner. In their formulation, it is Esav's inevitable death that renders the birthright valueless.

רשב"ם: הנה אנכי הולך למות - בכל יום אני הולך לצוד חיות ביערים המצויים שם דובים ואריות וחיות רעות ואני מסוכן למות למה זה לי להמתין [לקבל] חלק בכורה לאחר מיתת אבינו.

אבן עזרא: שבכל יום ויום הוא מסתקן בעצמו כאשר יצא לצוד שמא יהרגהו חיות ויתכן שימות קודם אביו.

Rashbam: Behold I am going to die - Every day I go out to trap animals in the forests where there are bears, lions, and wild animals, and I am in danger of death. Why should wait [to receive] the portion of the first born after the death of my father?

Ibn Ezra: Because every day he endangered himself when he went out to hunt, perhaps an animal would kill him and he would die before his father.

Thus, according to these commentators, the dangerous nature of Esav's activities made him wonder if he would live to benefit from the privilege of the birthright relating to the inheritance of his father. For this reason, he scorned the birthright in favor of a more immediate benefit. Ramban concurs with this analysis and brands Esav as one who lives only for today:

רמב"ן: וזו םיבת בזוי הבכורה כי אין חפץ בכסילים רק שיאכלו וישתו ויעשו חפצם בעתם ולא יחושו ליום מחר.

Ramban: And this is the reason for despising the birthright, for fools only want to eat and drink and fulfill their immediate needs without concern for tomorrow.

Did Ya'akov Take Advantage of Esav?

A simple reading of the text might imply that Ya'akov took advantage of Esav by withholding food from him in order to extricate the birthright from his possession. Rashi's explanation, on the other hand, suggests that the transaction was one of mutual consent in which each party seemed to benefit. The Zohar (pg. 139) records the following debate over this issue:

Once R. Shimon and his colleagues were sitting, and his son Eliezer entered. They said to R. Shimon: “We have a serious question to ask you regarding Ya'akov and Esav. How is it that Ya'akov did not want to give Esav lentil soup unless he would sell him his birthright? And not only this, but Esav said: ‘He tricked me twice.'” He said to them: “You are currently worthy of receiving lashes, for you believe the words of Esav and refute the words of Ya'akov, as the Torah testifies about him: ‘and Ya'akov was an unblemished person”, and it also says: ‘give truth to Ya'akov'. Rather, this is the matter of Ya'akov and Esav: Esav despised the birthright from the beginning and asked Ya'akov to take it from him, even at no cost, as the text states: ‘and Esav despised the birthright'.”

The suggestion of the Zohar that the food that Ya'akov gave to Esav was unrelated to the sale of the birthright seems inconsistent with the text. A close look at the grammar, however, lends support to the thesis of the Zohar. The verse that records that Ya'akov gave food to Esav utilizes the form “ויעקב נתן לעשו” rather than the usual Biblical form of the past tense “ויתן יעקב לעשו”. The former structure is recognized by some commentators as the past perfect form[2]which would be translated as “and Ya'akov had given to Esav” as opposed to the simple past which is translated as “and Ya'akov gave to Esav”. Thus, the verse would indicate that Ya'akov actually fed Esav before the transaction over the birthright. Furthermore, the Zohar implies that Ya'akov's suggestion for Esav to sell the birthright was not the initiation of the idea, but an attempt to compensate Esav for the birthright rather than taking it for free as Esav had suggested.

Conclusion

Whether it was Ya'akov or Esav that initiated the sale of the birthright, the commentators cited above all contend that Esav had an interest in giving up his claim to the birthright, either to reduce his level of responsibility or for immediate monetary gain. The story, as seen through the prism of the commentators, accents the difference in the character of the two brothers, a distinction that would play a role in their relationship throughout their lives.

[1] The Midrash on which Rashi is based (Bereshit Rabbah 63:13) also connects this idea to the wording

of the verse: “למה זה לי הבכורה” (“what is this to me the birthright”). The midrash explains that the seemingly superfluous phrase “זה לי” is a reference to the phrase in Shemot 16:2 – “זה אלי ואנוהו” (“This is my God and I will glorify him”), relating to one who dedicates himself to declaring God's praise, the divine service.

[2] Although Rashi does not refer to this point here, he describes this grammatical form in his commentary to Bereshit 4:1.