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 and given to the Tribe of Levi. 1
Rashi #2: When he asked Yaakov 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 - e.g. if they drank wine before serving, or if they had long hair. Esav said, 'I will die through it (i.e. I cannot adhere to all this)!' 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. Malbim - he said 'the Bechorah has no benefit in this world, and I do not believe in the world-to-come.'
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 (to 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? 3
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.
Gur Aryeh: How is such an interchange indicated in the Pasuk? Otherwise, how should we understand Esav's emphatic response!
Ha'amek Davar: Due to the dangers, he will die before his brother, who lives a calm life. After a Bechor dies, his sons have no authority over his living brothers. (Why was he not concerned for the time between his father's death and his own death? - PF)
Moshav Zekenim: He promised to give the Bechorah if Yaakov would advise him how to kill Nimrod, and Yaakov did so.
Remembering the day of death is the ultimate weapon against the Yetzer ha'Ra (Berachos 5a). Why did it not help for Esav?
Lev Eliyahu (Bereishis, p. 83): One who realizes that he will die, 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 Shema. These make one realize that only Torah and Mitzvos are important. Esav skipped these. Only physical pleasure was important to him.
QUESTIONS ON RASHI
Rashi writes: "... Esav said, 'I am going to die as a result; what do I need it for?'" The Gemara (Bava Basra 16b) derives from this verse that Esav denied Techiyas ha'Mesim. What is the derivation?
Maharal (Netzach Yisrael Ch. 15, p. 89): Esav's words, "Behold I am going to die," convey that this physical world was most important to him, and he had no desire for Kedushah. This shows he denied any future existence or resurrection of the dead.