And Avraham took cream and milk and the calf that he had prepared, and he placed them before the people, and he was standing over them under the tree, and they ate (18:8). Rashi comments, “And they ate”: They appeared to be eating. From here, we learn that a person should not deviate from custom, since these guests were angels who usually do not eat, they pretended as though they ate (Midrash Rabbah 48:14 and the Targum Yonasan). The opinion of the Shita Mekubetzes (Bachoros 6:2), who quotes the Yerushalmi and others that the angels indeed ate. The opinions of Midrash (Shohar Tov Tehilim 58 and Pesikta Rabasi chapter 55) are that the angels literally ate the meal. Therefore, the commentaries question that in the Posuk it states that Avraham prepared for them milk and meat, which is forbidden to meat in milk. The Torah forbids Bosor Becholov: A milk and meat mixture cannot be cooked together in one dish, or eaten, nor can any benefit or profit be derived from such a mixture. The Torah repeats three times the same verse: i ¦c §b l ¥y ©a §z ` l eO ¦` a¥l£g ©a (Shemos 23:19, and 34:26, Devorim 14:21). The stringency of their separation carries a rabbinical edict forbidding the eating of any dairy-meat mixture, even if they are not cooked together. Therefore, how were the angels permitted to eat the meal? The Shita Mekubetzes brings many answers. One 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, we still have to understand, according to both opinions, If angels don’t eat, why here did they eat or appear to eat? There is another difficulty in the Posuk, which states m²¤di ¥l£r "c ̄¥n r" `E «d §e and Avraham was standing over. Why does the Torah have to state that "c ̄¥n r" he stood over them when it could have simply said that Avraham prepared the food and they ate?
To address this difficulty: The Sefer Toras Yofeh (from Hagaon Rav Yechiel, the son of Hagaon Rav Nesanel Freid Rav of Besermin) brings a story from Rebbe Reb Elimelech of Lizensk l''wevf. The Rebbe used to travel to spread the teachings of the Baal Shem Tov. Once he was in a city and was the guest of melamed, who was very righteous but very poor. The melamed’s wife prepared Borsht, a soup of beets. Usually, people would add spices and fats to enhance the taste. Rebbe Elimelech ate the borsht and told his host that the borsht tasted excellent. When Rebbe Elimelech returned home, he told his wife how tasty the Borsht was that he ate at the melamed’s home. The Rebbetzin wanted to please her husband, and prepared borsht with different spices and fats and gave it to him to eat. However, Rebbe Elimelech said it doesn’t compare to the Borsht of the melamed's wife! The Rebbetzin was baffled and wanted to know what ingredients did the melamed’s wife put in the Borsht that her husband relished.
Determined to unveil the secret, the Rebbetzin visited Melamed's wife, who was delighted to meet her. They discussed the secret ingredients that made the borsht so tasty. The wife revealed that due to their poverty, they could not afford spices or fats for the borsht, therefore, when she made the borsht, she prayed to Hashem for the Holy Tzaddik to appreciate the simple dish, and as she prayed, tears streamed down her face, mixing with the borsht. She believed this was the essence the Tzaddik experienced. The Rebbetzin immediately comprehended the source of the taste and returned home.
The next day, she prepared Borsht and began to pray and cry that her husband should relish the Borsht, and her tears were mixed with the Botsht. After eating the borsht, Rebbe Elimelech exclaimed that the borsht was excellent, and he felt the Kedusha in the borsht.
Back to Avraham: The Gemara Berchos 26b says m ¥M §W©I©e":x ©n¡`¤P ¤W ,d ̈N ¦t §Y ` ̈N ¤` "d ̈ci ¦n£r" oi ¥` §e ,"m ̈W c©n ̈r x ¤W£` m ew ̈O ©d l ¤` x¤w A ©A m ̈d ̈x §a ©` l ¥N ©t§i©e q ̈g§pi ¦R c n£r©I©e" Avraham rose early in the morning to the place where he had stood before Hashem” (Bereishis 19:27), the verb c ©n ̈r means prayer, as this language is used to describe Pinchas’ prayer after the plague, as it is stated: l ¥N ©t§i©e q ̈g§pi ¦R c n£r©I©e “And Pinchas stood up and prayed and the plague ended” (Tehilim 106:30). According to this, we understand why Avraham stood over the angels. Avraham prayed that the guests should enjoy their meal, and tears flowed from him into the food. Therefore, when the holy angels saw this, they sensed the Kedusha in the food, which was enough for them to eat or appear to eat such holy food. Hence, the word "c ̄¥n r" he stood over them is the key. The secret to Oneg Shabbos at the Seuda, is when our cooks pour out their heart that the food should be worthy for the Shabbos meals. (Yehuda Z. Klitnick)