The angels knew exactly where Sarah was, so why did they ask Avraham where she was?
Rashi #1: It is good manners to ask one's host about the hostess, and one's hostess about the host. 1
Rashi #2 (citing Bava Metzia 87a): They wanted to endear Sarah to Avraham, when he would proudly answer that - modest woman that she was - she was in the tent, 2 because she knew that a woman's place is in the home.
Seforno: The purpose of the current Shelichus was to impart the good news to Sarah that she was about to conceive a son, so that she would rejoice and offer thanks to HaSh-m - thereby spiritually perfecting the conception.
Rashi #3 (citing Bava Metzia 87a): They wanted to send her the Kos Shel Berachah, upon which they had recited Birkas ha'Mazon. 3
We learn this from the dots on the letters 'Alef,' 'Yud' and 'Vav,' as Rashi explains. Hadar Zekenim explains that if only Sarah had been there, they would have asked "Ayo" (where is he, i.e. your husband). (However, Gur Aryeh understands that they in fact found an opportunity to ask Sarah as well; refer to 18:9:153:5).
Gur Aryeh: How do we know that this was their intent? The angels knew where Sarah was. Their question implied, "Why does she appear in our presence only for brief intervals of time;" from this Avraham would notice her modesty.
Why didn't Avraham himself send her the Kos? It is impolite to take food or drink away from a guest, to give it to a member of the household. Therefore, the guests inquired and sent the Kos (Gur Aryeh). Alternatively, Sarah had become a Nidah (Rashi to 18:8), and Avraham had hesitated to send it to her to prevent it from becoming Tamei (or due to Harchakos) (Sifsei Chachamim).
Men should not ask at all about women (Kidushin 70b)!
Riva #1: Angels are different.
Riva #2, citing Semag: One may not make her husband a Shali'ach to greet her, but one may ask her husband about her.
How do we expound the dots over the 'Alef,' "Yud' and 'Vav' in the word "Elav"?
Rashi: When there are more letters with dots, we expound them. When there are more letters without dots, we expound them. These letters spell the word Ayo, 'where is he (Avraham)?'.
According to Rashi, the Torah could have put dots just over the Lamed, and we would expound the other three letters! Why did it put dots on the other three?
Nimukei Yosef (Bava Metzia 52 DH Al Yedei): Had it put dots just over the Lamed, we would expound only "Ayo," that one asks a wife about her husband. Rashi (to Bava Metzia 87a DH Limdah) says that the dots uproot the word. I.e. since there are dots on three letters, we learn that they did not need to ask about Sarah, for they knew. They asked only because it is Derech Eretz.
Hadar Zekenim #1: It is not normal to begin with dots on just one letter. 1
Hadar Zekenim #2: Also, it might look like the Lamed is deleted.
Hadar Zekenim #3, R. Bechayei: A dot over the Lamed, together with the Zakef Katan (a cantillation Siman of two dots) over the Lamed, might look like 2 a Segol. 3
Gur Aryeh: The dotting indicates that these letters should be detached from the word, for this is not their true context. The angels did not ask Sarah, "Where is Avraham? (Ayo)" now, but rather earlier, when he was busy preparing the meal.
A Mishnah (Pesachim 9:2) says that there is a dot [only] on the Hei in 'Rechokah' (Bamidbar 9:10)! Maseches Sofrim (6:3) says similarly about 'u'Veinecha' (Bereishis 16:3) and 'uv'Kumah' (Bereishis 19:33)! Perhaps Rashi means that it is improper to begin, i.e. the first word in the Torah with dots should not have only on one letter. (PF)
Temanim write the Nikud above the letters. It seems that also others used to do so. (PF) Or perhaps, he refers not to the Nikud 'Segol,' but to the cantillation mark (Trup) by that name, which is written above the letter. (CS)
Pnei David: Minchah Belulah rejected this answer, for the dots are written in the Sefer Torah, but cantillation or vowels are not, and if they are written in a Sefer Torah they disqualify it (YD 274:7)! He did not see that R. Bechayei says this answer. (I can understand this answer only if the dots are mid'Rabanan. See, however, R. Chaim Paltiel (Shemos 17:9) and Me'iri (Kiryas Sefer 2:1) who maintain that they are a tradition from Sinai. (PF))
QUESTIONS ON RASHI
Rashi writes: "... They also asked Sarah, 'Where is Avraham?' This teaches that a person should inquire as to [the welfare of] his hosts - the wife from the husband, and the husband from the wife." But perhaps they simply did not know where Avraham went?
Gur Aryeh: They surely knew where Avraham was; he had greeted them upon their arrival.
Rashi writes: "This teaches that a person should inquire as to [the welfare of] his hosts - the wife from the husband, and the husband from the wife." But perhaps they asked Avraham about Sarah for one of the other two reasons Rashi mentions (to endear her to him, or to send her the Kos Shel Berachah)?
Gur Aryeh: We derive this rule of Derech Eretz (proper conduct) from what they asked Sarah regarding her husband Avraham (as derived from the dotted word Ayo), which had no other reason. Although it is usually improper for a man to inquire of a woman's welfare, the Gemara (Bava Metzia 87b) concludes that one may do so through her husband. We can therefore derive that it is Derech Eretz to ask the husband regarding his wife as well. 1
Gur Aryeh: This is why Rashi adds, "The angels knew where Sarah was! Rather.... it was to endear her to him... or, to send her the Kos Shel Berachah." This rule of Derech Eretz is derived solely from the fact that the angels asked Sarah regarding Avraham; that is why it is necessary to put dots above the word Ayo.
Rashi writes: "'Behold, [she is] in the tent' - She is modest." How do we know that this is what Avraham meant?
Gur Aryeh: The angels had not asked where Sarah was, but why she scarcely appeared during the meal (refer to 18:9:1:2*). If taken at face value, "Behold, she is in the tent" does not answer their question. Avraham answered that she did not show herself because she was modest.
Rashi writes: "A person should inquire from the wife as to [the welfare of]... her husband." But isn't it indecent for a man to listen to a woman's voice (Kol b'Isha Ervah - Berachos 24a, see Kidushin 70a)?
Gur Aryeh: Kol b'Isha Ervah means when his or her intent is to present or display her voice itself. It is permitted to speak normally with a woman (when there is a reason for doing so, such as in this case due to Derech Eretz). One must also avoid excessive conversation (Avos 1:5).
