To whom is Avraham speaking?
Rashi #1 and Seforno: To the senior of the three guests, 1 asking that he and his colleagues should enter his tent and partake of a meal, and not hurry to fulfill his mission, as is the way of important emissaries. 2
In which case, the word "Adonai" (with a 'Patach') is Chol, whereas according to the second explanation, it must be read with a 'Kamatz' and is Kodesh.
Even though this Pasuk is written after "And Avraham ran ..." otust hsave been said before.it. Even though in one context the Torah always preserves the order of events, this Pasuk must be rearranged (Riva citing Chizkuni). Or, even within one matter sometimes we are forced to say that the Torah is out of order (Riva citing R. Tam of Orleans). However, if we translate "va'Yomar" as 'And he had said',.the problem is solved.
Chochmah u'Musar (2 p.288): One cannot fathom the pleasure of receiving the Shechinah. How could Avraham interrupt to host guests? His pursuit of Mitzvos caused this.
Chazal learn from here that Hachnasas Orchim takes precedence over greeting the Shechinah. How can this be? The purpose was to increase Kevod Hashem and bring people under the wings of the Shechinah (Chochmah u'Musar 2 p.404). According to the Ramban, the guests only arrived after the Shechinah had departed.
Why must it say that he ran to greet them "mi'Pesach ha'Ohel" since that was where he was sitting?
Kol Eliyahu: One should not turn his back to his master. Rather, he leaves walking backwards. Avraham ran Likrasam (to greet the guests normally, facing them), even though he turned his back to the Shechinah. This is the source that hosting guests is greater than greeting the Shechinah (Shabbos 127a); they are not equal.