By way of introducing a question that Rabbi Simlai asked Rabbi Yohanan about the laws taught in the first two Mishnayot of our perek, the Gemara tells a story about their meeting.
Rabbi Simlai came before Rabbi Yohanan. He said to him: Would the Master teach me the Book of Genealogies? The Book of Genealogies was a collection of tannaitic teachings that formed a midrash on the Book of Chronicles. Rabbi Yohanan said to him: Where are you from? He said to him: From Lod. Rabbi Yohanan further asked: And where is your present place of residence? He said to him: In Neharde’a. Rabbi Yohanan said to him: I have a tradition that we teach these subjects neither to Lodites nor to Neharde’ans, and certainly not to you who comes from Lod and your residence is in Neharde’a, such that you have both shortcomings. Rabbi Simlai pressured Rabbi Yohanan until he agreed to teach him.
Rabbi Simlai said to him: Teach me the Book of Genealogies in three months. Rabbi Yohanan took a clod of dirt, threw it at him, and said to him: Berurya, wife of Rabbi Meir and daughter of Rabbi Hananya ben Teradyon, was so sharp and had such a good memory that she learned three hundred in one day from three hundred Sages, and nonetheless she did not fulfill her responsibility to properly learn the Book of Genealogies in three years because it is especially long and difficult. And you say that I should teach it to you in three months? After your inappropriate request, I am not inclined to teach you at all.
Faced with this final refusal, Rabbi Simlai asks the question on our Mishnayot, which Rabbi Yohanan agrees to explain to him.
Rabbi Simlai was one of the first generation amora’im in Israel, a student of Rabbi Yehuda Nesia and Rabbi Yannai. The Talmud, and, in particular, the Jerusalem Talmud, quotes him on matters of halakha, but he is better known for his many aggadic homilies.
The Book of Genealogies (Sefer Yohasin) discussed here is a collection of baraitot, a type of midrash on Divrei HaYamim. The Geonim explain that among the material included there were the genealogies of all the families mentioned in the book, something that can easily explain its length. The midrashim had information about which families were considered to have pristine backgrounds, and who had problematic histories. Rav Yehudah Leib ha-Levi Edel writes in his Iyye ha-Yam that we find very few midrashim on Divrei haYamim in the Talmud. Apparently all of the baraitot were in this collection, which included deep explanations of the personal names that appear in the book.
Our Gemara concludes that after a time Sefer Yohasin was lost. According to the Maharsha, there developed powerful families with “skeletons in their closets” whose secrets were found in the Sefer Yohasin, leading the Sages to refrain from teaching the work publicly, and it eventually fell from use. With its passing many of the secrets and traditions that it held were forgotten.