G-d appeared to him [Abraham]. (Gen. 18:1)
In the original Hebrew phrase, G-d's name appears last, literally reading: "Appeared to him G-d".
Why is Abraham, the subject of the vision, mentioned before G-d? The normal construction would have been "appeared G-d to him". In the previous visions Abraham received, G-d is always referred to first (compare 12:7 and 17:1). Why does the Torah not mention the nature of this vision, the subject matter discussed, etc.? Our sages in Talmud (Baba Metzia 86) say that G-d simply paid Abraham a visit, seeing the latter was still recovering from the effects of the circumcision. While this is a nice explanation, there is not a hint of this in the text.
Now that Abraham was circumcised, he was able to absorb a vision of G-d in His superior light….
I believe that the message to Abraham was that henceforth G-d's presence would rest on him on a permanent basis. In Kabbalistic terms, Abraham had now become a "carrier of the Shechina". The present form of address indicates that G-d's presence became felt by Abraham. Had the Torah used the usual wording we could not have become aware that G-d distinguishes between revelation itself and the One who reveals Himself. It is because of this that Abraham's future visions are never again introduced by the word for "appeared" ["veyera"]. We find only: "G-d spoke to Abraham". This is a reminder he already wore the "crown" indicating that G-d's presence was upon him.
The term "He appeared to him" also alludes to the letter yud of G-d's name becoming visible on Abraham's flesh as mentioned in Tanchuma 96 and Zohar I:95: "When the holy imprint rests on someone, this means that G-d's presence rests on that person."
The message is also that now that Abraham was circumcised, he was able to absorb a vision of G-d in His superior light. Not all became privy to a prophetic vision in the full sense of that word. He was able to absorb the full Four-Letter Name of G-d [Havayah]. We would not have understood this if the Torah had written: "And G-d appeared to Abraham" [in that order].
[Selected with permission from the five-volume English edition of "Ohr HaChaim: the Torah Commentary of Rabbi Chaim Ben Attar" by Eliyahu Munk.]