@BowsacNoodle I believe the three visitors to be symbolic of the Trinity, but not the actual Trinity. God the Father never appears in a form that can be reckoned by humans and if I recall He says to Moses later that He simply can't be seen, man would die from being faced with the Incomprehensible. Also, in the next chapter the two men with the Lord are explicitly referenced as angels. They are very beautifully symbolic of the Trinity however and at one point I believe they are referred to as acting as one. "They said" and so on.

Sarah's inner thoughts and the Lord's calling her out is an important bit to remember, especially when reading the gospels. The gospel writers, particularly Matthew, consistently call back to this interaction by using similar language. Someone thinks something "within themselves" then the Lord responds, "Why do you...?" The gospel writers saw Jesus as the same Lord that interacted with Abraham and the rest of the forefathers.