There is a difference in the definition of the word "an/a" and the word "the?" The chief grammatical function of "an/a" is to connote a thing NOT previously noted or recognized.
The little word "the" connotes a thing PREVIOUSLY noted or recognized.
Even Wallace, who quoted Acts 5:19 said it's "probably" the angel of the Lord which means he's not sure.
Re Genesis 16:7. This is the first appearance of the angel of the Lord AS the angel of the Lord. What does he tell Hagar at Genesis 16:10? "Moreover, the angel of the Lord said to her, "I will greatly multiply your descendants so that they shall be too man to count."
What does she say to him at Genesis 16:13. "The she called the name of the Lord who spoke to her, "Thou God does see me; for she said, Have I even remained alive here after seeing Him?"
The idea that the angel of the Lord multiplied Hagar's descendants begs the following question from Genesis 17:1-2, "Now when Abram was ninety-nine years old, the Lord APPEARED to Abram and said to him, "I am God Almighty; Walk before Me and be blameless, vs2, And I will establish My COVENANT between Me and you, And I will multiply you exceedingly."
Why does God Almighty allow the angel of the Lord to multiply Hagar's descendants but He clearly says at Genesis 17:1-2 that He will personally multiply Abraham's descendants? So is it possible that the angel of the Lord and God Almighty are one and the same being? Not one and the same person because the Bible makes a clear distinction of persons in both text of Genesis 16 and Genesis 17. And by the way, "the" angel of the Lord never appears as the angel of the Lord in the New Testament. He's mentioned but he does not function as the angel of the Lord.
