An insightful typological relationship unites the Theotokos with the miracle Moses witnessed in Horeb.
Every September 4 the Orthodox church celebrates the feast of the “Most Holy Theotokos the Unburnt Bush Icon.” Most commonly called “the Unburnt Bush Icon,” this iconographic depiction of the Virgin Mary is based on the miracle witnessed by Moses on Mount Horeb, as narrated in the book of Exodus: God calls Moses, while on Horeb, from a bush which “was burning, yet it was not consumed:”
Now Moses was tending the flock of Jethro his father-in-law, the priest of Midian, and he led the flock to the far side of the wilderness and came to Horeb, the mountain of God. There the angel of the Lord appeared to him in flames of fire from within a bush. Moses saw that though the bush was on fire it did not burn up. So Moses thought, “I will go over and see this strange sight—why the bush does not burn up.” When the Lord saw that he had gone over to look, God called to him from within the bush, “Moses! Moses!” And Moses said, “Here I am.” “Do not come any closer,” God said. “Take off your sandals, for the place where you are standing is holy ground.” Then he said, “I am the God of your father, the God of Abraham, the God of Isaac and the God of Jacob.” At this, Moses hid his face, because he was afraid to look at God.
Tradition understands the Unburnt Bush in the book of Exodus as being a type (that is, a prefiguration) of the Virgin Mary: just as the bush was burning without being consumed, the Virgin gave birth to Christ while remaining a virgin. Most of the Greek Fathers and early Ecumenical Councils agree in saying that when God spoke to Moses, Moses heard the pre-incarnate word of God (his Logos, as read in the opening lines of the Gospel of John), thus symbolically and typologically announcing his being born of the Virgin.
Most icons represent the bush and the flame symbolically, as two overlapping diamonds: a green one representing the bush, and a red one representing the flames. They both form an eight-pointed star (symbolizing the “Ancient of Days” the prophet Daniel often refers to), with the Theotokos (that is, the Virgin Mary) in the center holding the Child.