Exodus 3:5

And He said, Approach not hither, take the shoe from thy feet, for the place on which thou standest is a holy place; and upon it thou art to receive the Law, to teach it to the sons of Israel.

APPROACH NOT HITHER. Moses had not yet reached the highest degree of prophecy, for at Mount Sinai he drew near unto the thick darkness where G-d was. This also accounts for the hiding of his face [in this instance], for he had not yet reached that high [degree of prophecy of] which it was said of Moses, and the similitude of the Eternal doth he behold.

FOR THE PLACE WHEREON THOU STANDEST IS HOLY GROUND. Even though Moses was far from the bush, the angel warned him [not to approach], for the whole mountain became sanctified when the Divine Presence came down upon the mountain—top, just as it did at the time of the Giving of the Torah. Now Moses was on the mountain for he had ascended thereto, as it is said, and he came to the mountain of G-d, unto Horeb, and the bush was on the top of the mountain., that he was warned not “to approach.” Had he not been on the mountain at all, the warning should have been not “to come up.” Thus the entire site became holy and therefore the wearing of sandals was forbidden. A similar case is found in Joshua. Likewise, the priests ministered in the Sanctuary only while barefoot.

של!, throw off!. The word is from the root נשל, meaning a form of removal, as in Deuteronomy 7,1 ונשל גוים רבים, “He dislodges many nations, etc.”

של נעליך, even on the spot you are standing on now.

!של, “remove!” the reason why the Torah had to write: מעל רגליך, “from your feet,” when we all know that he was not asked to remove his sandals from his hands, is that there are two kinds of sandals. There is a kind worn on one’s hands. [In fact, in German, the word for gloves is: handschuhe, “shoes worn on one’s hands.” Ed.] This was the נעל that Boaz gave to the redeemer who was first in line to perform a levirate marriage ceremony with Ruth, the daughter-in-law of Naomi. (Ruth, 4,7) As far as the question why Moses had to remove both his sandals, whereas Joshua had to remove only a single sandal (Joshua 5,15), the reason is that in this instance the Presence of the Spirit of G–d preceded the arrival of Moses on that site, whereas in the Book of Joshua, Joshua had already been on holy soil (the land of Israel) before the appearance to him of the angel, i.e. the Spirit of G–d.