Adam Clarke on Hebrews 13:2

To entertain stranger's - In those early times, when there were scarcely any public inns or houses of entertainment, it was an office of charity and mercy to receive, lodge, and entertain travelers; and this is what the apostle particularly recommends.

Entertained angels - Abraham and Lot are the persons particularly referred to. Their history, the angels whom they entertained, not knowing them to be such, and the good they derived from exercising their hospitality on these occasions, are well known; and have been particularly referred to in the notes on Gen 18:3 (note); Gen 19:2 (note).