Charles Ellicott Commentary Genesis 18:4

"let now a little water be fetched, and wash your feet, and rest yourselves under the tree:" — Genesis 18:4 (ASV)

Wash your feet. —This is the first necessity of Oriental hospitality (Judges 19:21), not merely because the feet, protected only by sandals, are soiled by the dirt of the roads, but because it cools the whole body and allays the feverishness caused by the heat of travelling. Thus refreshed, they are “to rest,” Hebrew, to lay themselves down, in the shade.