What did Esav mean when he stated that the Bechorah was not for him because he was going to die?
Rashi: He played down the importance of the Bechorah, since in any event, the Avodah would eventually be taken away from the Bechoros would eventually be taken away from the Bechoros and given to the Tribe of Levi. 1
Rashi #2: When he asked Ya'akov what the Bechorah was all about, the latter informed him that it was about the Avodah, and that those who performed the Avodah were subject to the death-penalty - should they have drunk wine prior to going up to serve or if they not cut their hair. 2
Targum Yonasan: Connecting the Bechorah with the World to Come, he rejected it on the grounds that he would die in this world and not go to Olam ha'Ba anyway. 3
Seforno: He realized that, due to all his tiring activities, he would not live long, in which case the Bechorah was not worth anything.
Rashbam (citing his father), Da'as Zekenim and Ramban (Bereishis 25:34): Since, in his capacity as a hunter, he was constantly exposed to lions, bears and other wild animals, he was unlikely to live long. Consequently, what was the point of waiting to inherit his father?
Moshav Zekenim: He was close to death. Refer to 25:30:2:2.
Hadar Zekenim: He was destined to fight with Nimrod tomorrow, and feared lest he die. This is unlike the Perush that he was tired from killing Nimrod. 4
How he knew that however, is a mystery - seeing as he was not a Navi. Moreover, if he hadn't sold the Bechorah, his prediction would not have materialized.
Issues which one may assume that Esav would have had difficulty in adhering to.
This is synonymous with Esav's rejection of Olam ha'Ba and Techiy'as ha'Meisim (Pirush Na'ar Yonasan).
Moshav Zekenim: He promised to give the Bechorah if Yakov would advise him how to kill Nimrod, and Yakov did so.
Remembering the day of death is the ultimate weapon against the Yetzer ha'Ra (Brachos 5a). Why did it not help for Esav?
Lev Eliyahu (Bereishis p.83): One who realizes that he will die, he is zealous to use his time to acquire what is important. The first three weapons are to excite the Yetzer Tov, engage in Torah, and recite Shma. These make one realize that only Torah and Mitzvos are important. Esav skipped these. Only physical pleasure was important to him.
רש"י: מה טיבה של עבודה זו: מנין שאלה היו דברי עשיו?
גור אריה: אם לא כן, מה עניין "הנה אנוכי הולך למות" לכאן?!
רש"י: אמר אני הולך למות על ידה: מכאן דרשו שעשיו כפר בתחיית המתים, וצריך ביאור מנין דרשו כך?
מהר"ל (נצח ישראל פט"ו, עמ' פט, ד"ה ויש לך): "הנה אנכי הולך למות" משמעו שהעולם הגשמי הוא העיקר ולכן עשיו לא חפץ בקדושה, ומכאן שכפר בתחיית המתים.