Acts 7:33 NIV
Then the Lord said to him, 'Remove your sandals from your feet, for the place where you are standing is holy ground
The Lord tells us elsewhere to be holy because He is holy. The ground is holy because the Lord is present. If we stand with the Lord, we are on holy ground and this is the rock which will not be moved. All other ground is sinking sand.
The sandals could signify self, the material world, the pride and willfulness of the flesh.
Let us daily remove our sandals for we do indeed stand on holy ground.