At first Abraham seems to take his visitors as respectful travellers and calls them in for rest and refreshments. This would have been custom for godly people at the time, to show such hospitality to strangers. Abraham used the term “lord” for his leading guest, which in the NIV version of the scriptures refers to a common title of respect in Abraham’s time: like calling a man “sir” today. We don’t know if Abraham knew at first who he was entertaining. By verse 27 he used the more emphatic capitalised “Lord.”
It was probably the custom then to eat first before sharing the news the travellers had come to bring to Abraham. The lack of haste is refreshing in contrast to today’s standards. When it comes to visiting and to honouring guests, there is no hurry. The guests had to wait considerable time while food was being prepared. After eating the text says Yahweh shared the reason for his visit.
Abraham did not use the term “Yahweh,” but the text used Yahweh as the name of the angel who spoke to Abraham. The text also called Yahweh and the other two angels, “three men.” That is, Yahweh and the two angels appeared in human form. Yahweh is the name of the God of Israel. He is the almighty God, the creator, and in Isaiah “Yahweh” is used for the name of the supreme God and redeemer of Israel and redeemer of the world. In the Greek Septuagint translation of the Old Testament, Yahweh is translated Kū́rios, which was also used for Christ in passages like Philippians two, where it says, to Christ every knee shall bow. This also is a quote from Isaiah, showing that Paul referred to Christ as Yahweh.
There is no sense in the Genesis 18 text that this appearance of God in human flesh to Abraham and Sarah was an appearance of Christ as a distinct second person of the godhead. It is simply Yahweh, God in human form. The idea of theophany in the Old Testament, or the term Isaiah used – Emmanuel (God with us) – was common. God was present in creation in Spirit, Word and Light, present in the Exodus, present in the Torah, present in the tabernacle’s Holy of Holies, and present poetically in the Proverbs as Wisdom. In the incarnation, Christ is similar to all these Old Testament foretastes, but this time, God present in human form as son of man to redeem the world. This is why Jesus often spoke to the Pharisees as Yahweh. There was nothing un-Hebrew about this, not as far as the Old Testament was concerned. It was in this common Old Testament sense that the first apostles described God coming as Christ. We draw on this Hebrew traditional for understating the “trinity,” rather than the later Greek concepts.
Sarah was a partner in faith with Abraham, as the book of Hebrews later said, who also conceived by faith. They were “joint heirs” as Peter later put it, just as Adam and Eve were joint heirs in creation. Isaac was the seed of faith, meaning, as Paul said in Romans, that it is not the seed of the flesh or tribe that is significant. It isn’t Isaac verses Ishmael, but faith and service, verses race and self-boasting. The seed of faith is the seed of Abraham. This is why the promise is of faith, so that it might be sure to all the seed, from whatever nation. This overcomes the adversity of the flesh (tribalism), prevalent in the old Testament, to instead make us one in Christ and renew the nations.
Then the Lord contrasts Abraham with Sodom, saying he chose Abraham to lead him in the way of doing right, and his children after him, so that the Lord may bring to pass his promises on the earth. Even though Israel was imperfect, and the law was only a shadow of the good things to come, God was able to keep Israel until his final witness came in Christ.
We see the reluctance of God to judge, even utilizing the partnership of his friends to intercede on the behalf of the wicked. We see this also with Moses, when God said he would slay all Israel in the Wilderness, employing Moses’ intercession on their behalf. This doesn’t mean that Abraham and Moses are more merciful than God, but that God raises up priests within humanity to walk with him as covenant partners, and as witnesses of his mercy, judgement, and renewal. In a sense he was testing Abraham and Moses, to see if they knew God’s heart, to see what was in their own heart, and to teach mankind to plead with him for renewal rather than for judgment and bloodshed, teaching us to be his coregents. “I do not do anything unless I reveal it to my servants the prophets.” (Amos 3:7) This doesn’t mean prophets today know everything that is coming, but that God does give a witness before judgment comes. He takes no pleasure in the destruction of the wicked. Ezekiel 18:23