Commentary for Genesis 15:15

ואתה תבוא BUT THOU SHALT COME etc. Thou shalt not behold all this.

AND THOU SHALT COME TO THY FATHERS IN PEACE. And thou shalt not behold at this. Thus the language of Rashi.
This is not correct according to Rashi’s own interpretation, namely, that the decree, thy seed shall be a stranger in a land not their own,³²³Above, Verse 13. took effect as soon as Abraham had a child. Thus, soon after Isaac was born it states, And Abraham sojourned (‘vayagar’) in the land of the Philistines;³²⁴Further, 21:34. The word vayagar has the same root letters as geir (stranger), thus suggesting that Abraham lived as a “stranger” in a land which was not his own. And Isaac sojourned in Gerar.³²⁵Ibid., 26:6. The verse however states, vayeshev (and he “dwelled”), and not vayagar. In Rashi a different verse is quoted: Sojourn (‘gur’) in this land. (Ibid., Verse 3.) Now gur has the same root as vayagar. (See preceding note.) Now if so, Abraham was also included in the decree! But the meaning of the verse, And thou shalt come to thy fathers in peace, is that “no punishment will come to you from Me even though I decree on your children punishments of servitude and affliction.”

ואתה תבא אל אבותיך בשלום. As for you yourself, you will join your forefathers in peace. Why did the Torah interrupt the promises made to Abraham's descendants with a promise to Abraham personally? Even though G'd wanted to reassure Abraham that he personally would not experience the part of the decree connected with enslavement and oppression, this could have been stated after G'd had concluded telling him which generation would experience the redemption! The meaning would have been clear since the promise was adjoining the promise that Israel would experience redemption! Besides, why did the Torah have to repeat itself, stressing: a) "in peace," and b) "in a ripe old age?" Would it not have sufficed to promise Abraham that he would die in a ripe old age before the enslavement of his descendants would commence? The promise of death in a ripe old age would have implied that Ishmael would become a penitent, as pointed out by Bereshit Rabbah 38,12.