What happened to the bread that Sarah prepared?
Rashi: Sarah became a Nidah, 1 and the dough became Tamei - and Avraham, it seems, ate his Chulin b'Taharah. 2
Rashbam: It is so obvious that Avraham served it, that the Torah does not find it necessary to mention it.
Sifsei Chachamim: Her limbs felt heavy (indicating that she would soon become a Nidah), and she separated from the dough lest she be Metamei it. Before she found someone else to finish it, it became Chametz 3 (this took place on Pesach).
If so, why did she laugh at the idea that her Ednah (menstrual cycle, according to Rashi's second Peirush) would return? Tosfos (Rosh Hashanah 11b) answers, she thought that it was a fluke that she became Nidah, but not that her cycle was returning.
Bartenura: He would not serve to his guests something that he himself would not eat. Chasam Sofer (to Pesachim 46b) - it was Yom Tov of Pesach. Yisraelim may not bake on Yom Tov just for Nochrim ,if they themselves will not eat.
It is difficult to say that this is Rashi's intent, that "Tamei" means forbidden due to Chametz, amidst concern for Tum'ah (PF).
Why, according to Rashi, did Avraham see fit to prepare three bulls for his visitors?
Rashi (to 18:7, based on Bava Metzia 86b): In order to serve each one of them a tongue (the tastiest part of the animal) with mustard. 1
See Sifsei Chachamim for Rashi's source. Also refer to 18:7:1.3:1. According to Targum Yonasan and the Ramban, there seems to have been only one bull.
How could Avraham, who kept the entire Torah, serve his guests meat and milk during the same meal?
Rashi: He served the items in the order that he prepared them (as they appear in the Pasuk) - first milk and then meat. 1
According to the Gemara in Shabbos, it was precisely because the angels ate Basar b'Chalav that Moshe was able to convince them later that the Torah is meant for Yisrael and not for the angels.
Since when do angels eat?
What is the meaning of, "he was standing over them under the tree"?
Hadar Zekenim: Avraham was "ha'Gadol ba'Anakim" (a giant). He stood over them to make shade for them, like [as if they were under] a tree.
What is "the bull that he made"?
Da'as Zekenim: It means that he prepared it.
QUESTIONS ON RASHI
Rashi writes: "But the bread, he did not bring...." But perhaps Avraham did bring bread, and the Pasuk does not bother to mention it because of a Kal va'Chomer - if Avraham brought extra things that he had not offered them, certainly he brought the bread?
Gur Aryeh: One could have argued the opposite; if he brought even better fare, such as milk and butter, he might have exempted himself from the bread. Had the bread been served, it should have been mentioned.
Rashi writes: "As each item was prepared, he brought it before them." How do we know this; perhaps he brought out all the food at once?
Gur Aryeh: If so, it should say "the bulls" in plural. The singular indicates that he brought out one at a time, as soon as each one was ready.
Rashi writes: "... This shows that one should not deviate from the local custom." But perhaps they ate for the same reason that they had come - so that Avraham not be distressed over the lack of guests to serve?
Gur Aryeh #1: If not for the rule that they would not deviate from the custom (and would therefore appear to be eating), HaSh-m would not have sent angels (who do not usually eat).
Gur Aryeh #2: The verse could have said, "He placed [food] to eat before them." It adds, "and they ate" (i.e. appeared to eat), to teach not to deviate from the custom.
