Which two angels arrived in S'dom? What happened to the third angel?
Rashi (Bereishis 18:33) and Moshav Zekenim (18:22) #1: Gavriel came to overturn Sedom, and Refa'el came to save Lot. 1 Micha'el, whose mission (to inform Sarah of her impending birth) was accomplished, had returned to his heavenly abode.
Moshav Zekenim (Bereishis 18:22) #2: Gavriel came to overturn Sedom, and Micha'el came to save Lot.
Moshav Zekenim: An angel does only one mission, for there is no poverty in the place of wealth (it should not seem that Hashem lacks servants). Healing Avraham and saving Lot are like one mission.
Why does the Torah refer to them here as angels, and at the beginning of the Parshah, when they were with Avraham, as men?
Rashi #1: When the Shechinah was with them 1 it refers to them as men; when it was not, it refers to them as angels.
Rashi #2: In the presence of Avraham, who, in his greatness, was accustomed to seeing angels, it refers to them as men. In the presence of Lot, it refers to them as angels. 2
Why did it take so long for the angels to arrive in S'dom?
Rashi: Because they were angels of mercy, so they waited to see whether Avraham would succeed in obtaining a verdict of not guilty. 1
Seforno: They did indeed arrive much sooner 2 ; only they refrained from entering S'dom until Avraham their advocate had concluded his arguments.
How can Rashi (citing the Midrash) refer to Gavriel (who represents Midas ha'Din), who was coming to overturn S'dom) as 'angels of mercy'? Perhaps we can say that Hashem in His mercy, held the angels back until Avraham had finished.
Seforno: As the Gemara says in Berachos 4b 'Gavriel in two steps, Micha'el in one'.
Lot did not mind living in S'dom, in spite of (perhaps even because of) all its perversions. Moreover, he was not too fussy about idolatry (See Sifsei Chachamim). Why was he Moser Nefesh for guests, whom he did not even know?
Rashi: He had witnessed Hachnasas Orchim performed to perfection so many times by Avraham that it was second nature to him.
Seforno: With nowhere to stay, they would have slept overnight in the street, as was customary in those days - and Lot knew that the people of S'dom, would have molested them.
Why did Lot prostrate himself before the angels (although he did clearly not recognize as such)?
Seforno: Because, even in their human disguise, they must have been awesome in appearance. 1
Here the Torah says that Lot sat be'Sha'ar (at the gate) of S'dom. Above (in Lech'L'cha, Bereishis 14:12) it says that he sat in S'dom?
Rashi: Because be'Sha'ar" implies that he was a judge, and it was only on that day that he was appointed judge over them. 1 "
Moshav Zekenim: He entered the city itself due to the feud [with Avraham's shepherds, to distance from them]. Now he returned to his first place.
Rashi: That is why "Yoshev" is written without a 'Vav', so that we can read it "Yashav" (See Sifsei Chachamim)..