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. The places where the Lord deigns to appear to sinful men are ever afterward set apart in their eyes and may not be desecrated by irreverent behavior, for man owes to God the highest degree of veneration. Throughout the Orient, the custom of removing the shoes before entering into a place dedicated to divine service, whether true or false, is still observed.