1 Moses was keeping the flock of his father-in-law, Jethro, the priest of Mid'ian; and he led his flock to the west side of the wilderness, and came to Horeb, the mountain of God. 2 And the angel of the LORD appeared to him in a flame of fire out of the midst of a bush; and he looked, and lo, the bush was burning, yet it was not consumed. 3 And Moses said, "I will turn aside and see this great sight, why the bush is not burnt." 4 When the LORD saw that he turned aside to see, God called to him out of the bush, "Moses, Moses!" And he said, "Here am I." 5 Then he said, "Do not come near; put off your shoes from your feet, for the place on which you are standing is holy ground." 6 And he said, "I am the God of your father, the God of Abraham, the God of Isaac, and the God of Jacob." And Moses hid his face, for he was afraid to look at God. (Ex 3:1-6)
God is often imaged by fire. The reason is that everything that touches fire, becomes fire. When we enter into union with God, we share in God’s nature. Fire is a fair image of this. But there is a nuance to this, as described in this story. God manifested Himself to Moses in a bush that was on fire, but did not burn. The bush took on the nature of fire, but still retained the nature of a bush. That is, bush and fire were united, but each retained their own natures. So, when we enter into union with God, we are not annihilated. We retain our nature and our identity, while sharing in God’s nature.
This was imaged for us against at Pentecost:
3 And there appeared to them tongues as of fire, distributed and resting on each one of them. (Acts 2:3)
As Moses saw a fire resting on the bush, so that same fire rested on the Apostles. Again, they were not burned. Their nature was not changed. But, they enjoyed union with God, evidenced as they spoke in tongues. In both events, Christians recognize this unconsumming fire as a manifestation of the Holy Spirit.
Sacred Tradition offers us another consideration of the burning bush, related to Mary. The old Little Office of the Blessed Virgin Mary included this antiphon:
In the bush which Moses saw burning without consuming, we acknowledge the preservation of your admirable virginity, O Mother of God, intercede for us. (Lauds after Christmas, “Little Office of the B.V.M.,” Catholic Book Pub. Co., NY, 1962)
Several Fathers of the Church saw this: God entered into a physical union with Mary His Mother, yet He did not change her nature. Her nature was a young woman, a virgin; as she was before conception, so she was after: a virgin.
But there is a connection between the Incarnation and the Holy Spirit, such that the Holy Spirit “rested” on Mary, though without an image of fire. As we read in Luke, Mary was overshadowed by the Holy Spirit:
35 And the angel said to her, "The Holy Spirit will come upon you, and the power of the Most High will overshadow you; therefore the child to be born will be called holy, the Son of God. (Lk 1:35)
There are two phrases here, with two words we can explore. First is, “The Holy Spirit will come upon you.” The Greek word here translated as “come upon” is eperchomai. This word is used in Acts 1, when Jesus tells His Apostles about the coming of the Holy Spirit (Pentecost).
8 But you shall receive power when the Holy Spirit has come upon you; and you shall be my witnesses in Jerusalem and in all Judea and Sama'ria and to the end of the earth. (Acts 1:8)
The second phrase is, “the power of the Most High will overshadow you.” The Greek work here translated as “overshadow” is episkiazo. This word is also used in the Synpotic Gospels during the Transfiguration:
7 And a cloud overshadowed them, and a voice came out of the cloud, "This is my beloved Son; listen to him." (Mk 9:7)
As we know, this cloud is an image of the Holy Spirit. We see, then, a connection between the Holy Spirit “resting” on Mary at the Incarnation with similar images of the Holy Spirit overshadowing the Apostles at the Transfiguration and again at Pentecost.
We ourselves receive the Holy Spirit in Baptism, where water is sign of the sacrament. Why not fire as the sign, as the above images would seem to point? Of course, we can’t apply fire, which would injure; but fire is there, nevertheless, in every baptism:
11 I baptize you with water for repentance, but he who is coming after me is mightier than I, whose sandals I am not worthy to carry; he will baptize you with the Holy Spirit and with fire. (Mt 3:11)