“ויקח חמאה וחלב ובן הבקר אשר עשה, ויתן לפניהם” – “He took cream and milk and the calf that he had made, and set these before them.” The Gemara in Pesachim 50b discusses that which some are of the opinion is permitted, but others have the custom to prohibit those things, it should not be done in front of those who prohibit it. The Shach in Yoreh Dei’ah 119:20 says that if one comes from a place where the custom was to prohibit something, and one goes to a place where it is permitted, you are allowed to place that thing in front of them if it is clear what it is. This is what Avrohom Avinu did. Basar B’cholov, meat and milk, is now prohibited to be eaten together. However, before Matan Torah, it was permitted. However, although the Mitzvah of Basar B’cholov was not given to Avrohom Avinu, he nonetheless heeded all of the Mitzvos of the Torah, including Basar B’cholov even though these commands were not given yet. Avrohom Avinu did not know if these “guests” heeded the prohibition of Basar B’cholov or not. He therefore placed before them the meat and milk, so that it was clear and delineated, and then they could choose what they wanted to do. However, they did not seem to care, as the Posuk says, “ויאכלו” – and they ate it. They erred and should not have eaten it, and were embarrassed when Moshe sought to bring the Torah down and they tried stopping him. Moshe looked like Avrohom, and they then couldn’t say anything, as they had not kept the Torah that Moshe was holding, for they ate Basar B’cholov. With this understanding, we can explain Rashi. Rashi says that Sarah became Tamei, and she caused the bread that she made to become Tamei, and thus did not serve it. Many ask, what’s the difference if the bread was Tamei when they were eating Basar B’cholov? The answer is that Avrohom was not allowed to serve the bread to them, for it would not be apparent that the bread was Tamei – one could not clearly delineate by looking at the bread that it was Tamei. However, he was allowed to place the Basar B’cholov in front of them, for that was clearly delineated and they made their own choice.
