Gen 18:4

“But how does he continue again as if speaking to men: "Let water be received," the text says, "and your feet be washed"?Abraham, the father and teacher of nations, is indeed teaching you by these things how you ought to receive guests and that you should wash the feet of guests. Nevertheless even this is said mysteriously. For he knew that the mysteries of the Lord were not to be completed except in the washing of feet. But he was not unaware of the importance of that precept, indeed, in which the Savior says, "If any shall not receive you, shake off even the dust which clings to your feet for a testimony to them. Truly I say to you that it shall be more tolerable for the land of Sodom in the day of judgment than for that city." He wished, therefore, to anticipate that and to wash their feet lest perhaps any dust should remain, which, shaken off, could be reserved "in the day of judgment" for a testimony of unbelief. For that reason, therefore, wise Abraham says, "Let water be received and your feet be washed."”

“Moreover he adds, as though speaking to the men, "I will bring water, that you may wash your feet." Learn from blessed Abraham, brothers, to receive strangers gladly and to wash their feet with humility and piety. Wash, I repeat, the feet of pious strangers, lest there remain in them some dust that they will be able to shake off of their feet to your judgment. In the Gospel we read, "Whoever does not receive you—go forth and shake off the dust from your feet. Amen, I say to you, it will be more tolerable for the land of Sodom and Gomorrah in the day of judgment than for that town." Abraham foresaw this in spirit and for this reason wanted to anticipate it by washing their feet, lest perchance any dust remain that might be kept and shaken off on judgment day as an evidence of unbelief. Therefore the wise Abraham says, "I will bring water, that you may wash your feet." Carefully listen to this, brothers, if you are unwilling to exercise hospitality and to receive even your enemy as a guest. Behold, while blessed Abraham welcomed those men warmly, he merited to receive God in consideration of his hospitality. Christ further confirmed this in the Gospel when he said, "I was a stranger, and you took me in." Therefore do not despise strangers, lest perhaps he himself be the one you have rejected.”

“יקח נא LET BE FETCHED, I PRAY THEE — This implies bringing by a messenger: therefore did the Holy One, blessed be He, recompense his (Abraham’s) children by a messenger when they required water, as it is said, (Numbers 20:11) “And Moses lifted up his hand and smote the rock etc.” (Bava Metzia 86b) ורחצו רגליכם AND WASH YOUR FEET — He thought they were Arabians who worship the dust of their feet, and he was particular not to have the object of idolatrous worship brought into his house (Bava Metzia 86b). Lot, however, who was not particular about this, mentioned “lodging” (i.e. entering the house) before “washing” the feet, as it is said (Genesis 19:2) “[And he said to the angels] tarry here all night and wash your feet.” תחת העץ UNDER THE TREE — beneath the terebinth (Genesis Rabbah 48:11).”