When the Lord saw that he turned aside to look, God called to him from the midst of the bush and said, “Moses, Moses!” And he said, “Here I am.” Then He said,
“Do not come near here; remove your sandals from your feet,
for the place on which you are standing is holy ground.”
It was God's presence that made the ground around the burning bush holy. And when He departed it ceased to be holy. Because He is a holy God there will always be a distance between Him and man; we will never be equal with Him. The fact that we can have a relationship with Him shows His willingness to condescend to us.
Removing one's shoes is a sign of humility and reverence. "I doubt that Moses stooped to loosen his sandals. Like others who have beheld the glory of the living God, he may have fallen to the ground, prostrate. The flames which encompassed (but did not consume) the bush, along with the warning issued by the Lord from within the flames, emphatically impressed Moses with the holiness of the One who was manifesting Himself. Moses was deeply impressed with the holiness of his God." (Bob Deffinbaugh)
Too often humans have a flippant attitude toward God. May we, like Moses, be impressed with the holiness of our God.