Or HaChaim on Genesis 15:15/אור החיים על בראשית ט״ו:ט״ו

1 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.

2Righteous people, and especially our patriarchs, were always concerned with losing part of the reward they had stored up for use in the Hereafter through some act of kindness G'd would perform for them in this world. According to Bereshit Rabbah 44,4 Abraham worried that he might have caused the death of an innocent person in his war against the four kings and that as a result he had forfeited some of his eternal reward. G'd therefore reassured him by saying in 15,1: "Do not worry, your reward will be great." In view of the concern that Abraham displayed then it is reasonable to assume that he was similarly worried whether the eventual redemption from Egypt would not use up too many merits if it were accompanied by extraneous perks such as the רכוש גדול, acquisition of material wealth that would accompany it. What troubled Abraham was that clearly G'd would have to perform miracles in order to free his enslaved descendants when the time came. G'd wanted to put his mind at rest immediately; this is why He interrupted the prediction of what was going to happen by promising Abraham that his peace of mind would not be disturbed. The promise of שלום, refers to Abraham's peace of mind in the Hereafter, whereas the שיבה טובה, ripe old age, refers to his concerns about life on earth.