There are christians that say that Genesis 18 shows God coming down to earth in the flesh to meet with Abraham. As with many of their other claims, there is one major problem with this claim: Genesis 18 doesn’t say this.
I’m not going to write an essay on why the christian belief in a shape-shifting God is against the teachings and laws of the Jewish Bible. I’m just going to state a few facts about Genesis 18 and leave it there. My advice to you is to read the text in a good translation if you can’t read Hebrew, the more “literal”, the better. If you can read Hebrew, you’ve got no excuses.
1) God is never equated with the three men that appear to Abraham according to the text of Genesis 18. The first verse says that God appeared to Abraham, and verse two follows by saying that three men then appear. There is no textual phrase that makes the two occurrences one and the same.
2) None of the three men that meet Abraham are ever referred to as God or “Lord” in the divine sense according to the text of Genesis 18. This even includes verse 3 which has Abraham saying something, but it doesn’t make clear to whom according to the text. It doesn’t say “And Abraham said to one of the men, “Please, Lord, …” It doesn’t say this.
3) According to the text, the men come and then the men go, and God remains with Abraham. Textually, God was there before the men arrive, and remained a little while with Abraham after the men left.
With these three facts and actually reading the text through, there is no textual evidence in Genesis 18 that God became a man.