When Does a Son Become an Av: The Transfer of Spiritual Leadership from Avrohom to Yitzchok

The shiur opens with an apparent textual difficulty in Parshas Chayei Sarah. After the lengthy narrative of Eliezer's successful mission to bring Rivka back for Yitzchok, the Torah (תורה) inserts what seems like an irrelevant detail: "Vayitzchak ba mibon Be'er Lachai Roi" (Yitzchok was coming from Be'er Lachai Roi). Rashi (רש"י) explains he went to bring Hagar (Keturah) to Avrohom to remarry. But why is this information placed here, interrupting the story of Yitzchok's marriage? Similarly, the next passuk states "Vayeitzei Yitzchok lasuach basadeh lifnos erev" (Yitzchok went out to stroll in the field toward evening), which Rashi identifies as prayer. The Gemara (גמרא) learns from here that Yitzchok instituted tefilas Mincha. Again, why is this detail inserted at this precise moment in the narrative? Rabbi Zweig addresses a fundamental question that frames the entire analysis: Avrohom was 140 years old at this point, and he lived another 35 years until 175. Yet from this point forward, Avrohom almost completely disappears from the Torah. The only thing recorded about him is that he married Keturah and had children, and then he died. How can it be that a tzaddik as great as Avrohom, still physically vital (having children proves this), has nothing recorded about the last 35 years of his life? The same pattern repeats with Yitzchok—once Yaakov's story begins in earnest, Yitzchok disappears from the narrative except for the mention of his death.