Or HaChaim on Genesis 18:5/אור החיים על בראשית י״ח:ה׳

1 כי על כן עברתם על עבדכם, "for this is why you have come by your servant." These words were intended to silence the argument that once Abraham had recognised that his visitors were angels he should not have offered to give them human food. Although we explained that Abraham alluded to the spiritual nourishment the angels were to enjoy, this did not mean that we are to ignore the plain meaning of the verse. Terrestrial food also contains spiritually valuable ingredients as we know from Proverbs 13,25: "the righteous man eats to satisfy his soul." Abraham said to the angels that the reason they appeared in the guise of human beings was in order for them to partake of his food seeing that the spiritual content of that food also assumed the forms of the terrestrial world. The angels responded saying כן, yes, that Abraham was quite correct. They added that he should proceed as he had intended, i.e. to let them enjoy the spiritual content of the food.