Or HaChaim on Exodus 17:6/אור החיים על שמות י״ז:ו׳

1 הנני עומד לפניך, "I will be standing there before you, etc." The word לפניך refers to the place Moses was standing on when G'd spoke to him, whereas the word שם immediately afterwards refers to the rock. G'd emphasised that the whole earth is filled with His glory on a permanent basis and that He does not have to change location. However, there are sites where His presence is more manifest than in others. Alternatively, the degree in which G'd manifests Himself in certain locations is determined by the preparation that location has undergone in order to be a site fit for G'd to reveal Himself.