Adam Clarke on Genesis 19:1

Two angels - The two referred to Gen 18:22.

Sat in the gate - Probably, in order to prevent unwary travelers from being entrapped by his wicked townsmen, he waited at the gate of the city to bring the strangers he might meet with to his own house, as well as to transact his own business. Or, as the gate was the place of judgment, he might have been sitting there as magistrate to hear and determine disputes.

Bowed himself - Not through religious reverence, for he did not know the quality of his guests; but through the customary form of civility. See on verses Gen 18:3-5 (note) of the preceding chapter.