QUESTION: The Gemara discusses how David ha'Melech -- a descendant of Ruth, a Moavite convert -- became permitted to marry into the Jewish people. In a Halachic debate initiated by Shaul ha'Melech, Do'eg asserted that the Torah's prohibition against allowing converts from Moav to marry into the Jewish people applies equally to female converts as it applies to male converts. He argued that the reason the Torah gives for the prohibition against accepting male converts from Moav is that the men of Moav did not offer food to the Jews during their sojourn in the wilderness. Although it is not the manner for women to offer food to men, the Moavite women should have offered food to the Jewish women. Since the Moavite women did not offer food to the Jewish women, they are not to be accepted into the Jewish people.
The Beis Din was prepared to announce that David, a descendant of a female Moavite convert, was prohibited from marrying a Jewish woman, when Amasa spoke up and declared that he had heard from the Beis Din of Shmuel ha'Navi that a Moavite woman is permitted to join the Jewish people. Amasa added, "Anyone who does not accept this as Halachah will killed by the sword!"
What did Amasa intend to accomplish with his threat? The Halachah is that the members of one Beis Din may override another Beis Din's ruling if they have proof for their argument that disqualifies the other Beis Din's ruling. Here, Do'eg had a valid, logical argument. What evidence did Amasa have to refute Do'eg's argument?
ANSWER: The BRISKER RAV (Megilas Ruth) and the BEN YEHOYADA propose an explanation based on several rulings of the RAMBAM.
The Rambam (Hilchos Mamrim 2:1) writes that when a Beis Din issues a ruling based on the thirteen principles through which Torah law is derived, a subsequent Beis Din that determines that the thirteen principles should be applied differently may rescind the earlier Beis Din's ruling. This is based on the verse that obligates the people to follow the rulings of the Beis Din of their own generation, "who will be in those days" (Devarim 17:9; Rosh Hashanah 25b).
The Rambam earlier (Hilchos Mamrim 1:3) writes that a Halachah l'Moshe mi'Sinai cannot be subject to dispute. In his Introduction to Perush ha'Mishnayos, the Rambam adds that if Tana'im disagree about a certain point and one of them cites as proof a tradition received through a Halachah l'Moshe mi'Sinai, that proof is irrefutable and everyone must accept it.
The Rambam also writes (Hilchos Mamrim 3:2) that one who denies any part of the oral tradition ("Mesorah she'Ba'al Peh") is considered a heretic and permission is granted to execute him ("whoever kills him has done a great Mitzvah -- Asah Mitzvah Gedolah").
Finally, the Rambam (Hilchos Isurei Bi'ah 12:18) writes that the Halachah that a Moavite woman is permitted to join the Jewish people is a Halachah l'Moshe mi'Sinai.
Based on these rulings of the Rambam, the debate recorded in the Gemara here is understood.
Initially, the Chachamim were unaware of the Halachah l'Moshe mi'Sinai that permitted a Moavite woman to join the Jewish people. They thought that Shmuel ha'Navi had derived that ruling by applying the thirteen principles. Do'eg, therefore, was entitled to dispute the ruling based on his understanding of the thirteen principles. Amasa argued that no one is entitled to argue with Shmuel's ruling because it was not based on Shmuel's own reasoning and application of the thirteen principles. Rather, it was a tradition received as a Halachah l'Moshe mi'Sinai.
Accordingly, Amasa declared, "Anyone who does not accept this as Halachah will be killed by the sword," because a person who rejects a Halachah l'Moshe mi'Sinai, which is part of the Mesorah she'Ba'al Peh, has the status of a heretic and is liable to be executed, as the Rambam writes.
(Although the Gemara afterwards discusses the refutation to Do'eg's proof (why the Moavite women were not expected to greet the Jewish women and offer them food), it does so only to explain why the verse does not contradict the Halachah l'Moshe mi'Sinai. Its intention is not to explain the basis for why Moavite women converts are accepted today, for that indeed is a Halachah l'Moshe mi'Sinai.)
The Brisker Rav adds that the verse in Megilas Ruth relates that the Go'el did not want to marry Ruth "lest I will destroy my descendants" (Ruth 4:6). RASHI explains that the Go'el was concerned that his descendants would become prohibited to marry into the Jewish people because of the prohibition against accepting a Moavite woman (or her descendants) into the Jewish people. Why, though, was he concerned only about his descendants? If he maintained that a Moavite woman may not marry into the Jewish nation, he should have said that he did not want to marry Ruth because perhaps he might transgress the prohibition against marrying a Moavite convert! (MAHARSHA here; see IYUN YAKOV.)
The Brisker Rav answers that the Go'el thought that the Heter to accept a Moavite woman was based on the thirteen principles. Consequently, he was concerned that although the Beis Din in his generation decided that a Moavite woman convert is permitted, perhaps a later Beis Din will find an argument to refute that ruling and rule that a Moavite woman is forbidden to join the Jewish people. As a result, his descendants will become prohibited from joining the Jewish people retroactively. Therefore, he said that he cannot marry Ruth "lest I will destroy my descendants."
Bo'az, however, realized that the allowance to accept a Moavite woman convert was a Halachah l'Moshe mi'Sinai. (Indeed, the Beis Din of Shmuel is counted in the chain of trustees of the Oral Tradition, as recorded by the Rambam in his Introduction to Mishneh Torah.) As such, the law can never be revoked.
RAV YEHUDAH LANDY adds that even Bo'az did not realize at the time that the lenient ruling was based on a Halachah l'Moshe mi'Sinai. His confidence that no later Beis Din would revoke the ruling and prohibit a Moavite woman was based on a different reason.
The only basis to revoke the ruling would be Do'eg's argument, that the Moavite women were expected to greet the Jewish women, and since they did not do so they may not join the Jewish nation. The Gemara's answer to that argument is that women are not expected to go out to greet even other women, for they must conduct themselves with modesty and avoid public fanfare (see, however, the MAHARSHAL's explanation of the Gemara's answer).
It is reasonable to assume that Do'eg did not accept that argument because the attribute of modesty had no place in the mores of Moav. (On the contrary, promiscuity was the foundation of the Moavite nation, as Lot's daughter conceived her son, Moav, through her father and unabashedly publicized that fact in the name she gave her child; see Bereishis 19:37.) Bo'az, however, saw that Ruth excelled in the attribute of modesty (Rashi to Ruth 2:5, based on the Gemara in Shabbos 113b). He had firsthand proof for the veracity of the Gemara's response to Do'eg's argument; he saw that the Moavite women indeed had the potential for acting with modesty, and thus they had grounds on which to justify their lack of hospitality towards the Jewish women. Consequently, he felt confident in marrying Ruth.
(This approach also explains the Yerushalmi (Yevamos 8:3) which relates that Bo'az told Ruth, "Had you come two or three days earlier, you would not have been able to marry a Jew, for it is only now that we canonized the Halachah that a Moavite woman is permitted to marry a Jew." It was only because of the modesty which Ruth displayed that the courts ruled to allow Moavite women to join the Jewish people.)