Parshas Bamidbar:Megillas Rus

Rashi (Rus 4:6) explains that the Goeil doesn't want to fulfill teh mitzvah of yibum with Rus because he is worried that it will be a pegam on his children. The obvious question is that if the Goeil felt that it was assur to marry Rus because she came from Moav, why is he only concerned about his children-he should be worried about himself as well. He has no right to do an aveirah and marry Rus.

The Maharsha (Yevamos 77) answers that the Goeil felt the mitzva of Yibum is doche the issur of marrying a Moavis. How is there a mitzvah of Yibum? The Ramban in Vayeishev explains that the minhag kadmonim was that if a man died childless one of the man's male relative would marry the widow in order to perpetuate the dead man's name. This was the kavana behind Yehuda and Tamar. The Ramban adds that before Mattan Torah, any male relative would marry the widow. After Mattan Torah only a male relative who is muttar to marry the widow would marry her. The exception to this is obviously the dead man's brother where the Torah specifically allowed him to marry the widow. However, in a case where there was no brother it was the custom for any male relative (who is muttar to the widow) to marry the widow. The Ramban concludes that this is what happened with Boaz and Rus.

Therefore, the Maharsha writes that this aseh of Yibum was docheh the lav of Moavis. However, the Maharsha asks that the gemara tells us that really aseh docheh lo saseh would only apply to the first bi'ah. After that there is no aseh. Therefore, chazal made a gezeirah against doing bi'ah rishona so one won't come to do bi'ah shniah. In other words the klal of aseh docheh lo saseh would not apply to yibum. The Maharsha answers that perhaps the Goeil lived before the gezeirah and we would say aseh doche lo saseh.

However, the bottom line is Rus is still assur lavo bakahal. Even though bi'ah rishona is muttar, any child born from this union would be a Moavi and pasul to marry a Jew. This is why the Goeil refused to do yibum-he didn't want any child born from Rus to be pasul.

The Bereichas Ma'ayan asks on the Maharsha that the Ramban only writes it was a minhag to do yibum, he never says it is a mitzvas aseh. tzarich iyun on the Maharsha.


The Brisker Rav (al HaTorah on Rus) gives a more lomdishe answer. The Rambam paskens that one can not argue on Halacha L'Moshe Misinai. However a later beis din can argue and pasken against a halacha learned out of the 13 middos. Boaz held the derasha of Moav v'lo Moavis was Halacha L'Moshe Misinai. The Goeil was modeh to this. However, he was afraid that in a future generation there would be an assumption that this halacha is not Halacha L'Moshe Misinai.but rather it is learned from a drasha. Then a future Beis Din will disagree with the drasha and pasken a Moavis is pasul and his children will be pesulim. In fact that is what happened to Dovid HaMelech. (Yevomas 77). Do'eig argued that Moav v'lo Moavis is a drasha and he had questions against the drasha. Eventually Avner answered that it is a  Halacha L'Moshe Misinai and noone can argue against it,.