From Scratch, Patience 7 has it right. I will expand on her comments. Taken from my web-site,
www.seekfirstwisdom.com
The Greek Definite Article, "The, this, that," originally a demonstrative pronoun, but in Attic Greek, and in later usage mostly a prepositive article, (the," meaning the one and only, no other.)
1. As a demonstrative pronoun, "this, that."
1-a. Skimpily once in the words cited from the poet Aratus, Acts 17:28, "For we are also his offspring," for of this one (him,) we are also the offspring."
Jesus in the O.T. is at times referred to as, "The Angel of the LORD," or "Angel of Jehovah." Meaning He is revealing the will of His Father, as the #1 messenger. This appearance is called a, "Theophany," meaning "God appearing."
If you see, "An angel of the Lord," An, being an indefinite article, meaning more than one, it is making reference to other angels, or people.
The angel of God, is a title and office of Jesus, when He would temporally manifest Himself in a visible form in the O.T. Example:
Moses at the burning bush, Ex.3:2, "The angel of the LORD appeared unto him = (Moses) in a flame of fire out of the midst of a bush."
Ver. 4, now the angel of the LORD is called, "The LORD saw that he (Moses) turned aside, and see this great sight."
Then Scripture states, that it was God who called unto him = (Moses) out of the midst of the bush.
Then the voice said in
ver.5, "I am the God of thy 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 upon God."
Ver.7, "The LORD said." ver.8, "I am come down."
ver.14, "God said unto Moses, I Am that I Am."
Read through chap.4. So in this one example of the burning bush, the angel is called, The angel of the LORD, the LORD, God, and, I Am, that I Am. These are all offices, titles, and attributes of our Lord Jesus.
The LORD appeared to Abram many times. In Gen.21, Hagar the mother of Ishmael heard the voice of, "the angel of God," who said, "I will make him = (Ishmael) a great nation."
Judg.13:3, Zorah the mother of Sampson, had an encounter with the angel of the LORD. Also Judg.13:11-13-22-23, "Manoah (the father of Sampson) said unto his wife, We shall surely die, because we have seen God." Then his wife said, "if the LORD were pleased to kill us, He would not have received a burnt offering and a meat offering at our hands."
ver.19, where the angel of the LORD ate their offering with them. These are only a few examples of those who had physical, up close encounters with Jesus, "The angel of the LORD," in the O.T.
Hope this helps you.
Phil LaSpino