on bava kama 54b it says in the mishna that there are certain laws which the torah specifies particular animals such as ox or donkey and the law really applies to all animals. one of the laws that the mishna mentions is the law of animals staying away from har sinai. my question is: that law is a once in history law and never will apply again. therefore i thought that in cases where the law of a historic event isn't applicable to halacha for the future it isn't recorded or dealt with. many times when the gemara is bothered by a question of how a historic event took palce it just says "mah de'hava hava" what happened happened. so why in our mishna is it even mentioned that the law of the animals not touching har sinai applies to all animals? what's it's relevance to me?
The Tosfos Yom Tov (BK 5:7) seems to have been bothered by this problem and points out places where a similar difficulty is apparent.
The Tiferes Yisrael (ibid. note 59) suggests that the Mishnah teaches us the law in a case where someone says that he is Makdish the type of animal that was included in the restriction barring entrance to Har Sinai at the time of Matan Torah. A similar answer is found in the Ran in Sanhedrin (15b DH Shor) to a similar question.
The Meiri in Sanhedrin 15b quotes a Yerushalmi saying that the law forbidding animals to enter Har Sinai also applies to the Mishkan in Shiloh and the Beis ha'Mikdash. This being the case the Mishnah is teaching us a Halachah as to which animals are included by this law.
Dov Freedman