Why does the Torah write that "Hashem ascended from upon Avraham," rather than simply that "He departed from Avraham"?
Rashi #1: This is a more respectful way of speaking about Hashem. 1
Rashi #2 (based on Bereishis Rabah 47:6): This teaches that the righteous are the "chariot" (Merkavah) of Hashem. 2
Seforno: Aside from the precise wording, he explains that, as opposed to the Pasuk in Bereishis 4:15, which states that "Kayin left the presence of Hashem," here it was Hashem Who ascended from Avraham. This demonstrates Hashem's love for Avraham.
Gur Aryeh: In what way does the Torah alter its wording? The Shechinah was next to Avraham, and the Torah changes this and writes "upon" Avraham, meaning above.
QUESTIONS ON RASHI
Rashi writes: "We learn that the righteous are the 'Chariot' (Merkavah) of Hashem." Ramban asks
Gur Aryeh #1: Rashi understands that the three Avos represent a complete Merkavah, 1 whereas other individual Tzadikim are merely parts of a Merkavah, but not a whole one.
Gur Aryeh #2: Gur Aryeh himself prefers the print of the Midrash; only the Avos can be called a "Merkavah." This refers not only to the three Avos as a group, but each one of the Avos strove to excel at a particular Midah 2 (trait) of Hashem, and was a "whole" prototype for all those righteous people who would follow. 3
Ramban connects this to the Pasuk in Michah 7:20, which refers to "Emes l'Yaakov" and "Chesed l'Avraham." Chesed was the trait of Avraham, Pachad / Gevurah (fear) of Yitzchak, and Emes / Tif'eres (truth) of Yaakov, though Ramban intimates that this is a Kabalistic explanation that is beyond the ordinary person's comprehension.
Michtav me'Eliyahu (Vol. 2, Lech Lecha, p. 160): The Avos cleaved to Hashem with their entire hearts, even when they seemed to be tending to their mundane affairs. In turn, Hashem called His name upon them, and they were the Merkavah to the Shechinah. Avraham "carried" the trait of Chesed