Commentary for Genesis 48:21

הנה אנכי מת, although I am about to die, I am aware that after my death. והיה אלוקים עמכם והשיב אתכם אל ארץ אבותיכם, G’d will be with you and at the completion of 400 years predicted to Avraham will bring you back to the land of your fathers.

הנה אנכי מת, seeing that I make this my last will and testament when I am close to death, this gift is irrevocable.

ויאמר ישראל אל יוסף הנה אנכי מת, Israel said to Joseph: "I am about to die, etc." When Israel said: "I am about to die," he meant that only he was going to depart, the שכינה was not going to depart from them. Jacob added that G'd would lead the Jewish people back to the land of their ancestors. Jacob underlined that the land had been given by G'd to the patriarchs and not to the generation who would leave Egypt at the time of the Exodus. This being so, he was within his rights when he assigned Shechem to Joseph's descendants since he was the owner. When Jacob said: "and I have given to you one (extra) share, etc.," this is a valid explanation. Even according to the view of Rabbi Nechemyah in Bereshit Rabbah 97,6 that Jacob referred to the city of Shechem conquered by Shimon and Levi, Jacob implied that had it not been for the fact that G'd had given the land to the patriarchs they would not have succeeded.