Draw not nigh. The awful greatness of the Creator is such that his creatures, until invited to draw near, are bound to stand aloof. Moses, not yet aware that God himself spoke to him, was approaching the bush too close, to examine and see what the "great thing" was.
(See Exodus 3:3.) On the general unfitness of man to approach near to holy things, see the comment on Exodus 19:12. Put off thy shoes. Rather, "thy sandals." Shoes were not worn commonly, even by the Egyptians, until a late period, and would certainly not be known in the land of Midian at this time.
The practice of putting them off before entering a temple, a palace, or even the private apartments of a house, was, and is, universal in the East—the rationale of it being that the shoes or sandals have dust or dirt attaching to them.
The command given to Moses at this time was repeated to Joshua (Joshua 5:15). Holy ground. Literally, "ground of holiness "—ground rendered holy by the presence of God upon it—not "an old sanctuary," as some have thought, for then Moses would not have needed the information.