Charles Ellicott Commentary Genesis 18:1

"And Jehovah appeared unto him by the oaks of Mamre, as he sat in the tent door in the heat of the day;" — Genesis 18:1 (ASV)

And the Lord (Jehovah) appeared to him.—No new section could begin in this way, but evidently this is a continuation of the narrative of the circumcision. We thus find a Jehovistic section coupled in the closest way with one which is Elohistic ; and even here it is Elohim who for Abraham’s sake delivers Lot (Genesis 19:29).

Far more important, however, is to notice that this familiar interaction, and clear revelation of Jehovah to Abraham, ensues from his closer relation to God, which resulted from the sacrament of circumcision. Jewish tradition adds that this visit was made to Abraham on the third day after the rite had been performed, and was for the purpose of healing him from its painful consequences. For this reason, they think, Abraham was resting at home instead of being with his herds in the field.

The plains (Hebrew: the oaks) of Mamre.—(Genesis 14:13).

The tent door.—Hebrew: the opening of the tent, formed by looping back one of the curtains.

The heat of the day.—The time of noon, when Orientals rest from labor . As the air in the tent would be sultry, Abraham sits in the shade on the outside. So in Genesis 18:8 the meal is spread under a tree.