And the Lord appeared unto him in the plains of Mamre
That is, to Abraham; and very likely this appearance of God was quickly after the affair of the circumcision, to show his approbation of his ready obedience to his command; and at this time he was in the plains, or at the oaks of Mamre, the oaken grove there, as has been observed on ( Genesis 13:18 ) ; and which seems to be the best rendering of the words, since in ( Genesis 18:4 Genesis 18:8 ) ; mention is made of a tree to sit and stand under; and Abraham might choose this place for his habitation, because of the shadiness of it, in those hot countries:
and he sat in the tent door, in the heat of the day;
partly to cool and refresh himself, and partly to observe if any passengers passed by, to invite them in; this being a time of day when such needed refreshment, and it was proper for them to lie by a while, and not proceed on their journey until it was cooler: or rather to or "near" the tent door, as Noldius F7, or before it, without or under the shade of the tree, after mentioned.
The Brenton translation of the Septuagint is in the public domain.