What is the significance of the fact that Avraham asked for water to be fetched by a Shali'ach, and did not fetch it himself?
Rashi: Because it was on account of that that
Had Avraham fetched the water himself, it seems, Hashem would personally have provided Yisrael with water, and history would have taken a different turn. Note also that the bread and the meat he served directly - and that is why Hashem gave his children the Manna and the quails directly.
How do we explain the fact that whereas Avraham asked his guests to wash their feet before entering his tent, Lot did not (See in 19:2)?
Michtav me'Eliyahu (2, p. 241, from the Zohar): 'Washing their feet' refers to purifying themselves from their lowliness. Then, they can rest under the tree, i.e. the Eitz ha'Chayim (the interior of the Torah), and come under the wings of the Shechinah.
QUESTIONS ON RASHI
Rashi writes that what Avraham did for the angels, Hashem did for his descendants. The angels did not really need what Avraham did for them!