Why does the Torah see fit to inform us that Avraham went home?
Rashi: Once the Judge (HaSh-m) left the scene, 1 it was time for defense counsel to follow suit.
Seforno: The Torah is telling us that, unlike Kayin who left HaSh-m's presence, 2 Avraham waited (in prophecy-mode) until HaSh-m had departed, before he left.
Moshav Zekenim: Really, one cannot say that HaSh-m "left." It is a mere anthropomorphism.
See Bereishis 4:16.
QUESTIONS ON RASHI
Rashi writes: "Once the defense rested, the Judge left." Why does Rashi explain this?
Gur Aryeh: This entire phrase seems unnecessary, and needs to be explained.
Rashi writes: "Once the defense rested, the Judge left." But then the verse should say, 'Avraham finished speaking before HaSh-m;' when it actually says the reverse, "HaSh-m finished speaking to Avraham"!
Mizrachi: Perhaps this is a more respectful expression regarding HaSh-m.
Gur Aryeh: That would imply that Hash-m did not respond to Avraham's words. The verse makes it clear that first HaSh-m responded to Avraham, and only then He departed.
Rashi writes: "Avraham returned to his place' - The Judge left, so the defense left as well; and the prosecutor remained with his accusation." Why does Rashi say this here?
Gur Aryeh: This phrase in the verse explains the segue to the following verse (19:1). The angels had stalled for time, as Avraham tried to argue for Sedom. Only when he emerged empty-handed did they continue to Sedom to carry out their mission.