Moses saw a burning bush in which the fire did not consume the bush,
“When Moses saw it, he marveled at the sight; and as he drew near to observe, the voice of the Lord came to him, saying, ‘I am the God of your fathers—the God of Abraham, the God of Isaac, and the God of Jacob.’ And Moses trembled and dared not look. Then the LORD said to him, ‘Take your sandals off your feet, for the place where you stand is holy ground’” (Acts 7:31-33).
God was present. Therefore, the ground upon which Moses stood was holy ground. He needed to take his sandals off, for they had been walking upon the earth, bringing the filth of the world into the presence of God.
Moses needed to be aware of the presence, and Christians need to know that truth also, for our God is present everywhere.