Why did Yaakov see fit to mention his death here?
Seforno: He was substantiating the gift of a double portion that he had just given Yosef at the time of death. 1
Rashbam: He was reassuring Yosef that after his death, Hashem would have mercy on Yisrael, and that He would return Bnei Yisrael to Eretz Yisrael (as the Pasuk goes on to relate), after the 400 years that He had told Avraham expired.
Ohr ha'Chayim: Do not think that after I die, the Shechinah will depart from you. No; Elokim will still be with you!
Since a gift given at the time of death takes immediate effect.
Why did he say "Eretz Avoseichem"?
Ohr ha'Chayim: Eretz Kena'an was given to the Avos, and they acquired it; and not to those who left Egypt. Therefore, I am able to give to you "Shechem Echad" (48:22).
