And the angel of the LORD appeared unto him in a flame of fire out of the midst of a bush: and he looked, and, behold, the bush burned with fire, and the bush was not consumed.
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Augustine of Hippo
And here he is first called the angel of the Lord and then God. Is the angel then the God of Abraham, the God of Isaac and the God of Jacob? Therefore he may be rightly understood to be the Savior himself of whom the apostle says, “Whose are the fathers, and from whom is Christ according to the flesh, who is over all things, God blessed forever.” Hence even here he, who is the God blessed over all things forever, is not unreasonably understood to be himself the God of Abraham, the God of Isaac and the God of Jacob. But why was he previously called the angel of the Lord when he appeared in the flame of fire from the bush? Was it because he was one of many angels but by a dispensation represented the person of his Lord? Or was something belonging to a creature assumed which might appear visibly for the task at hand and from which words might be uttered in an audible way, whereby the presence of the Lord would also become known to the bodily senses of man, as circumstances required, by me...
It was not without reason, beloved brethren, nor without the signification of some mystery that there was a flame in the bush: “And the bush was not consumed.” Indeed, the bush was a genus of thorns. What the earth has produced for sinful man cannot be put in any kind of praise, for it was first said to man when he sinned: “Thorns and thistles shall the earth bring forth to you.” The fact that the bush was not burned, that is, was not seized by the flames, is understood to signify no good. In the flame is recognized the Holy Ghost; in the bush and thorns is represented the hard, haughty Jewish people.
When the almighty Lord of the universe began to legislate through the Word and decided to make his power visible to Moses, he sent Moses a divine vision with the appearance of light, in the burning bush. Now a bramble bush is full of thorns. So too when the Word was concluding his legislation and his stay among men as their Lord, again he permitted himself to be crowned with thorns as a mystic symbol. Returning to the place from which he had descended, the Word renewed that by which he had first come, appearing first in the bush of thorns and later being surrounded with thorns that he might show that all was the work of the same one power. He is one, and his Father is one, the eternal beginning and end. .
The bush which was unsuitable even as an image of dead gods was able to depict within itself the mystery of the living God. Moses, this is a sign to you: as you saw God dwelling in the midst of fire, by fire must you serve the God who dwells in the fire.
And when an angel appears to Moses, Holy Scripture also makes it plain, saying, “The angel of the Lord appeared to him in a flame of fire in a bush.” But when it refers to the actual being who replies, it calls him God and Lord and no longer an angel. It is equally clear in its distinction between the angel and the Lord in the account of what happened at the Red Sea. .
The Lord appeared. That is, and angel representing God, and speaking in his name. (Challoner) (Acts vii. 30; Galatians iii. 19.)
The apparitions of God to the patriarchs are generally understood in this sense. (St. Augustine, de Trin. iii. 11.) (Worthington)
Yet many of the Fathers suppose, that this angel was no other than the Son of God, the angel of the great council, (Malachi as iii. 1,) and St. Augustine (q. 2, in Ex.) does not disapprove of this opinion. (Calmet)
Not burnt. Thus the Hebrews were afflicted, but not destroyed. (Menochius)
God is styled a consuming fire, Deuteronomy iv. 24. He appeared in fire again, chap. xxiv. 17. (Calmet)
The vision and the voice are in the one place, nor is anyone else heard except the one who is seen. He who is an angel of God when he is seen is the same one who is the Lord when he is heard, but he himself who is the Lord when he is heard is recognized as the God of Abraham, Isaac and Jacob. When he is called the angel of God, it is revealed that this is not his true nature and that he is not alone, for he is the angel of God. When he is called the Lord and God, he is proclaimed as possessing the glory and name of his own nature. Accordingly you have in an angel who appeared in the bush him who is also the Lord and God.
What does this mean? The vision that is said to have appeared to Moses in the desert is sometimes called an angel, sometimes the Lord. It means this: he is called angel when he served by speaking externally, and Lord, because he ruled within and produced the conditions needed for speaking. For when the speaker is ruled from within, he is called both angel because of his service and Lord because of his inspiration. Exposition of the Old and New Testament, Exodus