Nowhere do we find that the angel returned!
Rashi #1 and the Ibn Ezra: The angel was speaking (not in his own name, 1 but) in the name of HaSh-m, who returned, despite the fact that the Pasuk does not mention it.
Rashi #2 (in Sefer ha'Pardes): He was hinting (not to the initial birth of Yitzchak, but) at his rebirth - at the Akeidah, where the same angel called out to Avraham to stay his hand.
Ramban: The angel was referring, neither to HaSh-m nor to himself, but to the turn of the year when the same time next year comes around, 2 as He promised him earlier (in 17:21).
What are the ramifications of the fact that the Torah writes "ka'Eis Chayah" with a 'Kamatz'?
Rashi: It means "you will be alive then (a year later), as you are alive now." 1
Moshav Zekenim, Rosh: Had it written k'Eis, with a Sheva, it would mean at the time for birth (nine months later). Gur Aryeh writes similarly.
Why did the Shunamis accuse Elisha of lying when (similar to the angels here), he promised her a baby at the same time next year (Melachim II 4:16)?
Rashi (citing Midrash Rabah): Because, unlike the angel, 1 Elisha did not promise that he would return the following year. Elisha replied that unlike the angels, he was a mere mortal, and there was no guarantee that he would be alive one year hence.
Why does the Pasuk suddenly switch from plural to singular (with reference to the angels)?
Rashi (to 18:2): Only one of the angels was sent to inform about the birth. 1
After informing us that Sarah heard the angel's words at the entrance of the tent, why does the Torah see fit to add that "Hu"(he or it) was behind the angel?
Targum Yonasan: The word "Hu" refers (not to the entrance of the tent but) to Yishmael, who overheard the angel's prophecy.
Seforno: It was because the entrance to the tent was behind the angel who was speaking that he did not speak to Sarah directly( as did Elisha to the Shunamis 1 ).
QUESTIONS ON RASHI
Rashi writes: "'I shall surely return' - It was not the angel [himself ] who promised to return, rather, he said this as a messenger of HaSh-m." What forces Rashi to explain this way?
Ramban: Later (18:14), HaSh-m Himself promises Avraham to return on the appointed day; it probably means the same here.
Gur Aryeh #1: In 18:14, it sounds like HaSh-m is coming to reinforce what was said in this verse; if so, the angel said the same thing.
Gur Aryeh #2: Angels are sent as needed, to fulfill an immediate task. The angel himself could not have committed to returning a year later. 1
Gur Aryeh notes that in (his edition of) Rashi, the comment on "ka'Eis Chayah" appears before the comment on "Shov Ashuv" (out of sequence with the Pasuk). Gur Aryeh explains that Rashi thus brings additional support to his interpretation of "ka'Eis Chayah" as referring to the next year (refer to 18:10:2:1), as Rashi will explain (Rashi to 18:14).
Rashi writes: "It was Pesach, and Yitzchak was born on the following Pesach." Why does Rashi need to add this?
Gur Aryeh: On the day of Avraham's Milah, HaSh-m had already promised, "Sarah will bear you Yitzchak at this time (Moed ha'Zeh) in the following year" (17:21). But now it was the third day since the Milah, and how can both dates be correct? Rashi understands that Yitzchak would be born precisely one year after the Milah; 1 this verse means that Yitzchak would be born in the Pesach season, albeit not on this exact calendar date.
Also see Rashi to 18:14.
Rashi writes: "It was Pesach, and Yitzchak was born on the following Pesach." There is an opinion in the Gemara that the angels' visit took place in Tishrei (refer to 17:21:151.1); how does that opinion interpret our verse (and verse 17:21)?
Maharal (Chidushei Agados Vol. 1, p. 98, to Rosh Hashanah 11a): In these verses, HaSh-m is not designating the date on which Sarah would give birth, but promising that by this date next year, Sarah will already have given birth. According to that opinion in the Gemara, the Milah and the subsequent visit by the angels took place in Tishrei, and Yitzchak was born approximately six months later, in Nisan. 1
Riva: Refer to 17:21:151.1:2.
Also refer to 17:26:1.1.
Rashi writes: "Yitzchak was born on the following Pesach." According to Rebbi Eliezer (Rosh Hashanah 10b-11a), Avraham and Yaakov were born in Tishrei. The angels visited Avraham (and told of Yitzchak's impending birth) in Tishrei, but Yitzchak was born in Nisan. Why was Yitzchak different in this way than the rest of the Avos?
Maharal #1 (Chidushei Agados Vol. 1, p. 96, to Rosh Hashanah 10b): "HaSh-m remembered (Pakad Es) Sarah" (21:1) in Tishrei, when she conceived; this was even more significant than Yitzchak's birth.
Maharal #2 (ibid.): In Tishrei, Midas ha'Din is at its strongest, and Yitzchak's trait was Midas ha'Din. 1 Birth does not reflect the full strength of Din, therefore his birth took place on Pesach, not Tishrei. 2
Maharal (Chidushei Agados Vol. 2, to Sotah 11b): We praise HaSh-m in the second Berachah of Shemoneh Esreh, which is the Berachah of Gevurah, as being 'Matir Asurim;' and this refers to His freeing a new baby from the confines of the womb! Perhaps Maharal means that conception more closely reflects Din / Gevurah than does birth. Also see Maharal (Gevuros Hashem Ch. 63) regarding the miraculous births that the Jews experienced in Egypt. (CS)
Rashi writes: "'v'Hu Acharav' - The entrance [to the tent, where Sarah was standing] was behind the angel." But perhaps the pronouns should be reversed - i.e. the angel was behind the entrance?
Gur Aryeh: An entrance (Pesach) is empty space; the terms 'behind' or 'in front of' cannot apply to it. Rather, it was the entrance of the tent that was behind the angel.
