Albert Barnes Commentary Exodus 3:5

"And he said, Draw not nigh hither: put off thy shoes from off thy feet, for the place whereon thou standest is holy ground." — Exodus 3:5 (ASV)

Put off thy shoes - The reverence due to holy places thus rests upon God’s own command. The custom itself is well known from the observances of the temple; it was almost universally adopted by the ancients and is retained in the East.

Holy ground - This passage is almost conclusive against the assumption that the place was previously a sanctuary. Moses knew nothing of its holiness after some 40 years spent on the Peninsula. It became holy by the presence of God.