And as to the shoes, let him who is about to touch the holy land which the feet of God hath trodden, put them off, as Moses did upon the mount, that he may bring there nothing dead; nothing to come between humanity and God (Gregory of Nazianzus, Oration 45.19)
As Moses stands in the presence of God on Mount Horeb, he is commanded to take off his shoes for the place on which he stands is holy. In the ancient Near East, the custom of taking off one's sandals was a sign of respect. But Gregory of Nazianzus turns our minds to the moral implications of what it means to stand in the presence of the holy. For Gregory, Moses' shoes signify those unholy things that stand between God and human beings. If any of us is to stand in the presence of the holy, we too must be holy. St. Augustine picks up on the same theme as well in Exodus 3:
What are the shoes? Well, what are the shoes we wear? Leather from dead animals. The hides of dead animals are what we protect our feet with. So what are we being ordered to do? To give up dead works. This is symbolically what he instructs Moses to do in his honor, when the Lord says to him, "Take off your shoes. For the place you are standing in is holy ground." There's no holier ground than the church of God is there? So as we stand let us take off our shoes, let us give up dead works (Sermon 101.7).
The story of Moses and the burning bush is one of calling. Moses is being called by God, and the people are being called too-- out of their bondage to a place of freedom where they will live as God's people. The foundation of the divine law is the holiness of God, which God's people are to reflect in their lives. It is no accident that holiness is connected to the call; for the call cannot be fulfilled without throwing off what is dead within us, that which keeps us away from the holy presence of God, that which interferes with the charge we have been given to keep.
St. Paul tells, the Colossians,
So if you have been raised with Christ, seek the things that are above, where Christ is, seated at the right hand of God. Set your minds on things that are above, not on things that are on earth, for you have died, and your life is hidden with Christ in God. When Christ who is your life is revealed, then you also will be revealed with him in glory.
Put to death, therefore, whatever in you is earthly: fornication, impurity, passion, evil desire, and greed (which is idolatry). On account of these the wrath of God is coming on those who are disobedient. These are the ways you also once followed, when you were living that life. But now you must get rid of all such things—anger, wrath, malice, slander, and abusive language from your mouth. Do not lie to one another, seeing that you have stripped off the old self with its practices and have clothed yourselves with the new self, which is being renewed in knowledge according to the image of its creator. In that renewal there is no longer Greek and Jew, circumcised and uncircumcised, barbarian, Scythian, slave and free; but Christ is all and in all!
As God’s chosen ones, holy and beloved, clothe yourselves with compassion, kindness, humility, meekness, and patience. Bear with one another and, if anyone has a complaint against another, forgive each other; just as the Lord has forgiven you, so you also must forgive. Above all, clothe yourselves with love, which binds everything together in perfect harmony. And let the peace of Christ rule in your hearts, to which indeed you were called in the one body. And be thankful (3:1-15).
Israel's wanderings in the wilderness will be the result of their lack of trust in God; their lack of holiness. In refusing to cast off the dead things, God's people often found themselves at odds with the living God on their way to the Promised Land
Holiness is not an option; it is but another name for the image of God reflected in God's people. The Bible says that without holiness, no one can see the Lord (Hebrews 12:14). It is also the case that without holiness no one can see Lord reflected in the Lord's people.