Jamieson, Fausset and Brown on Exodus 3:5

5. put off thy shoes--The direction was in conformity with a usage which was well known to Moses, for the Egyptian priests observed it in their temples, and it is observed in all Eastern countries where the people take off their shoes or sandals, as we do our hats. But the Eastern idea is not precisely the same as the Western. With us, the removal of the hat is an expression of reverence for the place we enter, or rather of Him who is worshipped there. With them the removal of the shoes is a confession of personal defilement and conscious unworthiness to stand in the presence of unspotted holiness.