It should not surprise us that God would reveal Himself to Abraham in the image of man any more than we are surprised that God would "create man in His own image".
A few years ago I was present at a luncheon of Christians and Jews in which a friendly exchange of questions and answers was taking place. In a gracious way, Jews were challenging Christians and Christians were challenging Jews. I opened my Bible to Genesis 18 and waited for an opportunity to quiz the Rabbi leading the discussion. This passage talks about God’s revealing Himself to Abraham in the form of three men. But I never got to ask my question. Instead, the Rabbi referred to the incident himself–but without explaining the dilemma–and from that point on never surrendered the floor for anyone else to speak. Finally, I realized the dear man was so afraid of having to answer inquiries about God appearing in the form of three men that he would not allow any more inquiries. I understand his crisis. This passage radically challenges unitarian theology.
Those who have difficulty accepting the reality of God revealing Himself in multiplicity should take heed to the manner in which He displayed Himself to Abraham. Those of us who embrace the doctrine of the Holy Trinity are not saying there are three gods, we are saying that the One, all-sovereign Being who created our Universe three-dimensionally can reveal Himself in that same trinitarian way if He so chooses. Not only so, but science has confirmed other dimensions beyond the one we presently know. Heaven is such a dimension.
Genesis 18:1-19:2: Then the Lord appeared to him (Abraham) by the terebinth trees of Mamre, as he was sitting in the tent door in the heat of the day. So he lifted his eyes and looked, and behold, three men were standing by him; and when he saw them, he ran from the tent door to meet them, and bowed himself to the ground,
20. And the Lord said (to Abraham), "Because the outcry against Sodom and Gomorrah is great, and because their sin is very grave, I will go down now and see whether they have done altogether according to the outcry against it that has come to Me; and if not, I will know." Then (two of) the men turned away from there and went toward Sodom, but Abraham still stood before the Lord.
Genesis 19: 1: Now the two angels came to Sodom in the evening, and Lot was sitting in the gate of Sodom. When Lot saw them, he rose to meet them, and he bowed himself with his face toward the ground.
The revelation of God to Abraham is this:
1. "The Lord appeared to him." (Yahweh) in the form of
2. "Three men were standing by him ..." naashiym
3. "The men turned away ..." haaªnaashiym but,
4. "Abraham still stood before the Lord." (Yahweh)
5. "Two angels came to Sodom ..." Shaneey (two)  hamal’aakiym (angels)
In God’s plural appearances to Abraham we have one of the most theologically challenging examples of deity sovereignly transitioning His nature between the Divine, the angelic, and human essence, at will. We are introduced to this mystery in the opening chapter of Genesis where--in every instance and more than 30 times--the name of God appears only in the plural. The personal pronoun, "we, our" is used consistently.

6. No matter how we divide it, it is the Lord, who appears to Abraham--but in three distinctly divisible components. He is one in three manifestations. As is water capable of composing itself as a solid, liquid, or a gas. So also, the physical world is three-dimensional.
Abraham may never have realized the honor God gave him that day in revealing to him the Trinitarian nature of God. We have this same witness all around us in that the physical Universe is three-dimensional. — John the Baptist never knew that he was the promised ‘Elijah who was to come’".
Genesis 1:1-2. "In the beginning God created the heavens and the earth. The earth was without form, and void; and darkness was on the face of the deep. And the Spirit of God was hovering over the face of the waters."
God = 'elohiym = plural noun. Created = bara' = a singular verb.
In Hebrew when the plural noun is used for the God of Heaven it is accompanied by a singular verb. When the same noun is used for other gods it is always accompanied by plural verbs.
Matthew 28:1-7. AN ANGEL: Now after the Sabbath, as the first day of the week began to dawn, Mary Magdalene and the other Mary came to see the tomb. And behold, there was a great earthquake; for an angel of the Lord descended from heaven, and came and rolled back the stone from the door, and sat on it. His countenance was like lightning, and his clothing as white as snow. And the guards shook for fear of him, and became like dead men. But the angel answered and said to the women, "Do not be afraid, for I know that you seek Jesus who was crucified. He is not here; for He is risen, as He said. Come, see the place where the Lord lay. And go quickly and tell His disciples that He is risen from the dead, and indeed He is going before you into Galilee; there you will see Him. Behold, I have told you."
Mark 16:1-7. A YOUNG MAN: Now when the Sabbath was past, Mary Magdalene, Mary the mother of James, and Salome bought spices, that they might come and anoint Him. Very early in the morning, on the first day of the week, they came to the tomb when the sun had risen. And they said among themselves, "Who will roll away the stone from the door of the tomb for us?" But when they looked up, they saw that the stone had been rolled away — for it was very large. And entering the tomb, they saw a young man clothed in a long white robe sitting on the right side; and they were alarmed. But he said to them, "Do not be alarmed. You seek Jesus of Nazareth, who was crucified. He is risen! He is not here. See the place where they laid Him. But go, tell His disciples — and Peter — that He is going before you into Galilee; there you will see Him, as He said to you."
Luke 24:1-6. TWO MEN: Now on the first day of the week, very early in the morning, they, and certain other women with them, came to the tomb bringing the spices which they had prepared. But they found the stone rolled away from the tomb. Then they went in and did not find the body of the Lord Jesus. And it happened, as they were greatly perplexed about this, that behold, two men stood by them in shining garments. Then, as they were afraid and bowed their faces to the earth, they said to them, "Why do you seek the living among the dead? 6 He is not here, but is risen!
John 20:11-15. TWO ANGELS: But Mary stood outside by the tomb weeping, and as she wept she stooped down and looked into the tomb. And she saw two angels in white sitting, one at the head and the other at the feet, where the body of Jesus had lain. Then they said to her, "Woman, why are you weeping?" She said to them, "Because they have taken away my Lord, and I do not know where they have laid Him." Now when she had said this, she turned around and saw Jesus standing there, and did not know that it was Jesus.
John 1:1-5. "In the beginning was the Word, and the Word was with God, and the Word was God . He was in the beginning with God. All things were made through Him, and without Him nothing was made that was made. In Him was life, and the life was the light of men. And the light shines in the darkness, and the darkness did not comprehend it.
John 17:5-6. "And now, O Father, glorify Me together with Yourself, with the glory which I had with You before the world was ."
John 17:20-21. "I do not pray for these alone, but also for those who will believe in Me through their word; that they all may be one, as You, Father, are in Me, and I in You; that they also may be one in Us, that the world may believe that You sent Me.
John 17:24-25. "Father, I desire that they also whom You gave Me may be with Me where I am, that they may behold My glory which You have given Me; for You loved Me before the foundation of the world.
1 Peter 1:18-20. "Knowing that you were not redeemed with corruptible things, like silver or gold, from your aimless conduct received by tradition from your fathers, but with the precious blood of Christ, as of a lamb without blemish and without spot. He indeed was foreordained before the foundation of the world, but was manifest in these last times for you.
 Colossians 1:15-21. He is the image of the invisible God, the firstborn over all creation. For by Him all things were created that are in heaven and that are on earth, visible and invisible, whether thrones or dominions or principalities or powers. All things were created through Him and for Him. And He is before all things, and in Him all things consist. And He is the head of the body, the church, who is the beginning, the firstborn from the dead, that in all things He may have the preeminence. For it pleased the Father that in Him all the fullness should dwell, and by Him to reconcile all things to Himself, by Him, whether things on earth or things in heaven, having made peace through the blood of His cross.
Daniel 3:24-26. Then King Nebuchadnezzar was astonished; and he rose in haste and spoke, saying to his counselors, "Did we not cast three men bound into the midst of the fire?" They answered and said to the king, "True, O king." "Look!" he answered, "I see four men loose, walking in the midst of the fire; and they are not hurt, and the form of the fourth is like the Son of God"
To the great One in three,
Eternal praises be,
Hence evermore,
His sovereign majesty,
May we in glory see, And to eternity,
Love and adore!