the Lord appeared - another manifestation of the divine presence, more familiar than any yet narrated; and more like that in the fulness of time, when the Word was made flesh.
plains of Mamre - rather, terebinth or oak of Mamre; a tall-spreading tree or grove of trees.
sat in the tent door - The tent itself being too close and sultry at noon, the shaded open front is usually resorted to for the air that may be stirring.