On The Holy Trinity by St. Augustine
Chapter 13.--The Appearance in the Bush.
23. But when Moses was sent to lead the children of Israel out of Egypt, it is written that the Lord appeared to him thus: |Now Moses kept the flock of Jethro his father-in-law, the priest of Midian: and he led the flock to the back side of the desert, and came to the mountain of God, even to Horeb. 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. And Moses said, I will now turn aside, and see this great sight, why the bush is not burnt. And when the Lord saw that he turned aside to see, God called unto him out of the midst of the bush, and said, I am the God of thy father, the God of Abraham, the God of Isaac, and the God of Jacob.| He is here also first called the Angel of the Lord, and then God. Was an angel, then, the God of Abraham, and the God of Isaac, and the God of Jacob? Therefore He may be rightly understood to be the Saviour Himself, of whom the apostle says, |Whose are the fathers, and of whom as concerning the flesh Christ came, who is over all, God blessed for ever.| He, therefore, |who is over all, God blessed for ever,| is not unreasonably here understood also to be Himself the God of Abraham, the God of Isaac, and the God of Jacob. But why is He previously called the Angel of the Lord, when He appeared in a flame of fire out of the bush? Was it because it was one of many angels, who by an economy [or arrangement] bare the person of his Lord? or was something of the creature assumed by Him in order to bring about a visible appearance for the business in hand, and that words might thence be audibly uttered, whereby the presence of the Lord might be shown, in such way as was fitting, to the corporeal senses of man, by means of the creature made subject? For if he was one of the angels, who could easily affirm whether it was the person of the Son which was imposed upon him to announce, or that of the Holy Spirit, or that of God the Father, or altogether of the Trinity itself, who is the one and only God, in order that he might say, |I am the God of Abraham, and the God of Isaac, and the God of Jacob?| For we cannot say that the Son of God is the God of Abraham, and the God of Isaac, and the God of Jacob, and that the Father is not; nor will any one dare to deny that either the Holy Spirit, or the Trinity itself, whom we believe and understand to be the one God, is the God of Abraham, and the God of Isaac, and the God of Jacob. For he who is not God, is not the God of those fathers. Furthermore, if not only the Father is God, as all, even heretics, admit; but also the Son, which, whether they will or not, they are compelled to acknowledge, since the apostle says, |Who is over all, God blessed for ever;| and the Holy Spirit, since the same apostle says, |Therefore glorify God in your body;| when he had said above, |Know ye not that your body is the temple of the Holy Ghost, which is in you, which ye have of God?| and these three are one God, as catholic soundness believes: it is not sufficiently apparent which person of the Trinity that angel bare, if he was one of the rest of the angels, and whether any person, and not rather that of the Trinity itself. But if the creature was assumed for the purpose of the business in hand, whereby both to appear to human eyes, and to sound in human ears, and to be called the Angel of the Lord, and the Lord, and God; then cannot God here be understood to be the Father, but either the Son or the Holy Spirit. Although I cannot call to mind that the Holy Spirit is anywhere else called an angel, which yet may be understood from His work; for it is said of Him, |And He will show you things to come;| and |angel| in Greek is certainly equivalent to |messenger| in Latin: but we read most evidently of the Lord Jesus Christ in the prophet, that He is called |the Angel of Great Counsel,| while both the Holy Spirit and the Son of God is God and Lord of the angels.