Genesis 18:1-2 And the LORD appeared unto him in the plains of Mamre: and he sat in the tent door in the heat of the day; And he lift up his eyes and looked, and, lo, three men stood by him: and when he saw them, he ran to meet them from the tent door, and bowed himself toward the ground,
Genesis 18:13-14 And the LORD said unto Abraham, Wherefore did Sarah laugh, saying, Shall I of a surety bear a child, which am old? Is any thing too hard for the LORD? At the time appointed I will return unto thee, according to the time of life, and Sarah shall have a son.
Genesis 18:17-18 And the LORD said, Shall I hide from Abraham that thing which I do; Seeing that Abraham shall surely become a great and mighty nation, and all the nations of the earth shall be blessed in him?
John 8:56-58 Your father Abraham rejoiced to see my day: and he saw it, and was glad. Then said the Jews unto him, Thou art not yet fifty years old, and hast thou seen Abraham? Jesus said unto them, Verily, verily, I say unto you, Before Abraham was, I am.
The (Old) Testament contains numerous appearances of God in the form of a man, sitting, speaking, even eating with those that love Him.
Abraham was sitting in front of his tent on the plains of Mamre, when the LORD (Yehovah -- Yud Hay Vav Hay) came to him and declared the fulfillment of a promise He had made to him many years before, saying that through Abraham's seed the world would be blessed! (Genesis 12:7; 13:15-16, 15:18, 17:7-9) For a long season, the Patriarch had patiently waited for the fulfillment of this promise, but it wasn't until the LORD came to him personally, speaking face to face, that the fulfillment of this promise drew near. No wonder Yeshua (Jesus) told the Jews of his day that Abraham rejoiced to see Him! It was the day that the promise -- the long awaited promise -- was coming to pass!
The visitation of God, the Creator of the universe, to this Earth, in the form of a man, seems preposterous to normal human understanding; yet we know it is true, historical, and certain because God has revealed it to us by His Spirit and His Word. Because of this astounding Incarnation, every other promise of the Word is absolutely reliable. Faith and patience are all that are necessary for us to receive them. Is there anything too hard for the LORD? Follow the example of our Father Abraham and stand on the WORD He has given you. Every one of His promises will be fulfilled....... in His time!