Reading the Torah, I noticed that when the angels, disguised as travelers, visited Abraham, he served them "butter and milk and the calf which he had prepared." Isn't this a violation of the prohibition against eating meat and milk together?
a. A simple answer would be that this story took place before the Torah was given at Mount Sinai, and the kosher laws--as well as all other Torah laws--were not yet binding. However, the Talmud tells us that Abraham kept all of the Torah, including the kosher laws, even though he was not commanded to do so.
b. A careful look at the verse shows that Abraham did not actually dine with his guests. Rather, he served the butter, milk, and meat to people whom he believed to be traveling gentiles (there were no other Jews back then), and were obviously under no dietary obligations. Abraham saw no reason that his personal stringencies should diminish the enjoyment of his guests.
What about the angels? How could they eat non-kosher? According to one opinion, the angels didn't eat at all; they merely appeared to be eating, out of respect for their host.
There is, however, a Midrash which contends that this was no show of etiquette; the angels actually ate meat and milk together. Years later, when Moses was about to be given the Torah, the angels protested, saying that mortal man does not deserve G‑d's greatest treasure, the Torah. Moses, in typical Jewish fashion, answered a question with questions of his own, and asked the angels (among other things), "You knew the Torah. Did this stop you from indulging in a mixture of milk and meat at Abraham's place?" The angels had no reply, and the rest is history. For more on that altercation, see The Sinai Files.
c. Some commentaries point out that the verse indicates that Abraham first served dairy and then the meat. Jewish law specifies that one may eat meat immediately after dairy (except for certain aged cheeses), provided that one adequately cleans one's mouth and hands between the two. See Waiting Periods Between Meat and Dairy for the details. Hence, the meal was in compliance with the kosher laws.
Rabbi Baruch S. Davidson