Genesis 18 tells of a fascinating series of events in which three men appear to Abraham, and one of them speaks to Abraham as the LORD and promises Abraham that they will return the next year and Sarah will bear a son in her old age. Abraham then walks with the three men for a time as they continue on their way, and God reveals to Abraham the coming destruction of Sodom and Gomorrah. All of these things transpire just as the man said. So who were these three men? The Jewish Talmud identifies them as three angels, and many Christians see them as an appearance of the Trinity: that all three men represented the one true God. Neither of these explanations, however, fits the text. The reality is that in this amazing passage, God appears to Abraham along with two angels, all with their glory veiled in a human form. These same two angels that appear with God to Abraham are the ones that go on to deliver Lot and his family out of Sodom before God destroys the city. From the rest of Scripture, we can know that the one who appeared to Abraham was specifically God the Son, the pre-incarnate Christ.
The passage opens:
"Now the Lord appeared to him by the oaks of Mamre, while he was sitting at the tent door in the heat of the day. When he lifted up his eyes and looked, behold, three men were standing opposite him; and when he saw them, he ran from the tent door to meet them and bowed himself to the earth," (Genesis 18:1-2).
So we know right off that the sudden appearance of these men represents the Lord appearing to Abraham. Most of the rest of the passage is Abraham talking with the Lord as he dines in his home with the men and then walks with them as they head on toward Sodom. The passage goes on to state:
"Then the men turned away from there and went toward Sodom, while Abraham was still standing before the Lord," (Genesis 18:22)
It may be tempting to read this as saying that all three men left and that the LORD was still there speaking with Abraham independent of the men. The rest of the passage, however, shows us that two of the men went on while one remained speaking with Abraham. The one who remained was the LORD, while the other two were angels. After conversing with Abraham further about the coming judgment of the cities below, the passage concludes by telling us that:
"As soon as He had finished speaking to Abraham the Lord departed, and Abraham returned to his place. Now the two angels came to Sodom in the evening as Lot was sitting in the gate of Sodom. When Lot saw them, he rose to meet them and bowed down with his face to the ground," (Genesis 18:33-19:1)
The LORD departs, Abraham goes home, and the two angels arrive at Sodom. That accounts for all three men who were walking with Abraham. And note that the passage doesn't just say that two angels arrive in Sodom, but rather that the two angels arrive. These are the two angels that the story has already introduced. The two angels who were walking with Abraham and God. So the three men who appeared to Abraham were God and the two angels who were then sent on to Sodom before judgment came to that city.
Now, John 1:18 explains that:
"No one has seen God at any time; the only begotten God who is in the bosom of the Father, He has made Him known."
Paul also tells us that the Father, "dwells in unapproachable light, whom no man has seen or can see," (1 Timothy 6:16) and that Jesus is the "image of the Invisible God," (Colossians 1:15). The only consistent conclusion that we can come to is that whenever the LORD, Jehovah God, has appeared before the eyes of men, it was the Son of God who appeared. No man has ever seen God the Father. He has always been made known by God the Son, the eternal Word who ultimately became flesh in Jesus Christ (John 1:14) and perfectly revealed God once and for all. This is the marvel of the Triune God of the Bible. He is a God whom no man can see and yet who has been seen, with no contradiction! God the Father remains gloriously veiled from our sight while God the Son appears to us and makes the Father known and God the Holy Spirit works within us that we may understand. This is the only way we can grasp the incredible historical event recorded in Genesis 18, where God appeared as a man for a moment to promise a miraculous son, who in turn foreshadowed a time when God would appear as a man in Christ Jesus who would come as a miraculous, promised Son!