John Chrysostom

He did not say, "Be hospitable," as if they were not, but, "Be not forgetful of hospitality," for this was likely to happen owing to their afflictions.

Therefore (he says) "some have entertained angels unawares." Seest thou how great was the honor, how great the gain!

What is "unawares"? They entertained them without knowing it. Therefore the reward also was great, because he entertained them, not knowing that they were Angels. For if he had known it, it would have been nothing wonderful. Some say that he here alludes to Lot also.

And he did not say, "Be not forgetful" of the entertaining of strangers, but "of hospitality": that is, do not merely entertain strangers, but do it with love for the strangers. Moreover he did not speak of the recompense that is future, and in store for us, lest he should make them more supine, but of that already given. For "thereby some" (he says) "have entertained angels unawares."