Among the angels in the Bible, there is one special angel we hear about in the Old Testament: The angel of the Lord. The special thing about Him is that He is called the angel of the Lord and not just an angel of the Lord. This shows that this is a special angel, whom we meet only at some places in the Old Testament.
The angel in the Old Testament
So Who is this special angel? One of the things which is very special about Him is the fact that He is equated with God in more than one text. For example when Moses is being called by God we read:
“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.“(Exodus 3:1-6)
The same equation with God we see in Judges 6:11-25. In this history, the angel of the Lord is also called the Lord (see also Judges 13, 1 Chronicles 21:16-17).
On the other side, we also hear how the angel of the Lord speaks to the Lord and is addressed by the Lord:
“Then the angel of the Lord said, “Lord Almighty, how long will you withhold mercy from Jerusalem and from the towns of Judah, which you have been angry with these seventy years?” So the Lord spoke kind and comforting words to the angel who talked with me.” (Zechariah 1:12-13)
The angel in the New Testament
In the new Testament we no longer meet the angel of the Lord (in Luke 2 we hear about an angel of the Lord).
So who is this special angel? Because of His equation with the Lord Himself, many Christians believe it is Christ before His incarnation (His becoming flesh, human, as Jesus of Nazareth). This explains His equation with the Lord. At the same time this also explains that He can be different from the Lord as in the vision of Zechariah 1, because God the Son is not the same as God the Father, though they are also one, together with the Holy Spirit. Finally, this also explains that we do not hear about the angel of the Lord in the New Testament, since He has become flesh and we know his name: Jesus Christ, the Son of God, our Lord and Mediator.