What is the significance of the burning bush? In Exodus 3, God reveals himself to Moses through the sign of a burning bush, which miraculously is not consumed by the flames. Here is Exodus 3:1-6 in the NRSV:


  Moses was keeping the flock of his father-in-law Jethro, the priest of Midian; he led his flock beyond the wilderness, and came to Horeb, the mountain of God. There the angel of the Lord appeared to him in a flame of fire out of a bush; he looked, and the bush was blazing, yet it was not consumed. Then Moses said, "I must turn aside and look at this great sight, and see why the bush is not burned up." When the Lord saw that he had turned aside to see, God called to him out of the bush, "Moses, Moses!" And he said, "Here I am." Then he said, "Come no closer! Remove the sandals from your feet, for the place on which you are standing is holy ground." He said further, "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.


Why does God choose to use the sign of the burning bush, as opposed to any other miracle?

It seems to me that there should be some reason why a blazing (but not consumed) bush in the middle of the wilderness is particularly appropriate for the message that God was delivering to Moses. I was also wondering whether there is a specifically Christian interpretation of this event, given the other parallels between the Exodus and the work of Jesus.
There is a concept found throughout the Old Testament that God is a consuming fire:


  Deuteronomy 4:24 (NIV)
  For the LORD your God is a consuming fire, a jealous God.


The idea behind this consuming fire is that it is the fire of God's judgment.  Just before that verse in Deuteronomy, it says not to make idols (starting in verse 24) because the God is a consuming fire.  We can see pretty clearly that this fire is a picture of God's judgment and wrath.

By comparison, one thing that is striking about the image of the burning bush is that there is fire that does not consume.

This is showing us that the imagery of the burning bush is one of mercy.  The consuming fire engulfs the bush, but the bush is not consumed.  The judgment is brought, but mercy is shown.

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Another theory is that the burning bush indicates that Israel will not be consumed by the upcoming plagues in Egypt.  It was, the theory goes, a way to indicate to Moses that there will be fires and judgments but the nation will not be consumed.

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A final, simpler theory is simply that God used an item that was present at that time in that location (a bush in the desert) to indicate his glory.  The fire that burned was simply his glory illuminating the bush.  (Fire, at that time, was the only known source of light besides the sun.)

Source (same as previous)