Who was the “Angel of the Lord” mentioned so often in Scriptures?
The word “angel” simply means a “messenger of God” for a messenger from God and in both the Old Testament and the New Testament, angels are always messengers of God or His representatives, depending upon the situation. Angels are powerful spirit  beings that can, with God’s command, appear in human form. One angel is powerful enough to kill 185,000 soldiers in one quick passing (2 Kings 19:35) so this may be why the author of Hebrews writes “Do not neglect to show hospitality to strangers, for thereby some have entertained angels unawares” (Heb 13:2). God will sometimes use angels to bring us messages like the coming destruction of Sodom and warning Lot and his family (Gen 19) and if someone tries to interfere with the angel’s commission, then that could lead to serious consequences (Gen 19:11) so is there a difference between the angels of the Lord and “the” angel of the Lord?
Before Abraham Was
Jesus existence didn’t begin in Bethlehem. He has always existed (John 1:-2) and there is nothing that exists that was not created by Him (John 1:13) so He could not have been created. Those who believe Jesus was the angel Michael do not have the right Jesus and without the right Jesus, you don’t have the right Savior. Jesus told the Jews, “Truly, truly, I say to you, before Abraham was, I am” and the Jews knew that God’s name was “I AM, “So they picked up stones to throw at him, but Jesus hid himself and went out of the temple” (John 8:58-59). When Paul was writing to the Corinthians about the ancient Israelites he wrote that “all drank the same spiritual drink. For they drank from the spiritual Rock that followed them, and the Rock was Christ” (1 Cor 10:4). The great “I AM” statements of Jesus match what God did with ancient Israel in the wilderness…and beyond, so we can clearly see that Jesus was, long before Abraham was…and before all things existed and speaking of Jesus Christ, Paul writes, “For by him all things were created, in heaven and on earth, visible and invisible, whether thrones or dominions or rulers or authorities—all things were created through him and for him” (Col 1:16).
The Angel of the Lord
I believe there is a vast difference between “the angel of the Lord” and “an angel from the Lord” because “the” angel seems very specific and it’s not just any angel, but “the angel” of the Lord, and many scholars believe that this was the pre-incarnate Christ. The first reference to “the angel of the Lord’ was when the angel came to Hagar, Abraham’s mistress and her son, Ishmael and said to her “Behold, you are pregnant and shall bear a son. You shall call his name Ishmael” (Gen 16:11), “So she called the name of the Lord who spoke to her, “You are a God of seeing,” for she said, “Truly here I have seen him who looks after me” (Gen 16:13). Notice that Hagar called this “angel” the Lord who spoke to her” (Gen 16:13). But, was it Jesus, the Father, or the Holy Spirit?
God, Man or an Angel?
When Jacob had an encounter with what was called “the angel of God” in Genesis 32,he wrestled with “a man” who told Jacob, “Your name shall no longer be called Jacob, but Israel, for you have striven with God and with men, and have prevailed” (Gen 32:28) and since God alone changes names in the Bible, this must have been God Himself in the appearance of a man because Jacob said, “I have seen God face to face, and yet my life has been delivered” (Gen 32:30). Was it the face of a man or the fact of God? Jacob, now called Israel , called Him God. During the campaign to rid Israel of all of the inhabitants of Canaan, Joshua “lifted up his eyes and looked, and behold, a man was standing before him with his drawn sword in his hand. And Joshua went to him and said to him, “Are you for us, or for our adversaries” (Joshua 5:13) but the man said, “’No; but I am the commander of the army of the Lord. Now I have come.’ And Joshua fell on his face to the earth and worshiped and said to him, ‘What does my lord say to his servant’” (Joshua 5:14) and “And the commander of the Lord’s army said to Joshua, ‘Take off your sandals from your feet, for the place where you are standing is holy.’ And Joshua did so” (Joshua 5:15). This must have been a pre-incarnate encounter with the living God. Whether it was Jesus or not, we’re not told, but we know it must have been God because Joshua was told the very same thing that Moses was told when he was in the presence of the Lord, for example in Exodus 3:5 God told Moses in the burning bush, “Take off your shoes for this is holy ground” (Ex 3:5).
Clearly, the angel of the Lord is not the same as an “angel from the Lord,” because the angels are sometimes mentioned by name (Michael or Gabriel) or referred to as simply “an angel,” but “the angel of the Lord” and “an angel from the Lord” cannot be the same thing every time. Most Bible scholars believe that this must have been the pre-incarnate Christ Who made appearances from time to time in the Old Testament and when we look at all of the Scriptures referring to “the angel of the Lord” we can conclude that this is God Himself and that God enters into human history and intervenes by whatever means He sees fit.
Read more about angels here: Bible Study on Angels 
Resource – Scripture quotations are from The Holy Bible, English Standard Version® (ESV®), copyright © 2001 by Crossway, a publishing ministry of Good News Publishers. Used by permission. All rights reserved.