Yismach Moshe

"And wash your feet" (Bereshit 18:4). See Rashi (s.v. "and wash"). The Kli Yakar asked: Why should the light of the sun enter his house? Many people worship the sun! Rather, it is not prohibited, for it is ground of the world, and such ground is not prohibited (Sanhedrin 47b). End of quote. In my view there is no difficulty at all. Rashi wrote that they bow down to the dust on their feet because it would have been enough to say simply that they bow down to dust. But in his sweet language he meant to resolve the above question. In truth, ground of the world is not prohibited. But once the dust clings to a person's feet, it is detached from the ground, and when they bow down to it, it becomes prohibited and is idolatry. Therefore Avraham was careful that this dust not enter his house, as explained above.