Moses to Joshua, from Joshua to the elders, from the elders to the prophets, until they were finally committed to writing about the middle of the second century by Rabbi Judah, surnamed "the Holy." According to the general received opinion of at least the greatest portion of the Jewish people, the Mishna contains God's explanation of the Written Law and is held by them of equal sanctity, but having been handed down orally, it is hence called the Oral Law. The explanations or precepts contained in the Mishna enter into the minutest detail how the various commandments in the Pentateuch are to be observed. Thus, for example, with respect to the proper observance of the Sabbath day, the Mishna contains a treatise of no less than twenty-four chapters, in which are enumerated thirty different kinds of principal occupations, and subdividing itself in innumerable minor works which are forbidden to be performed on that day.
Now in a similar manner in the treatise Yebamoth, which treats on the obligations of a brother marrying the childless widow of a deceased brother, and of the ceremony connected with it, and on other matrimonial laws in general, a vast number of regulations are laid down explanatory of the Mosaic laws recorded in Lev. xviii. xx. and Deut. xxv., and among them in chapter x. § 4 of that treatise the following rules are laid down, which are no doubt intended to be explanatory of Lev. xviii. 18. "If a man, whose wife is gone to a country beyond the sea, is informed that his wife is dead, and he marries her sister, and after that his wife comes back, she may return to him. * * After the death of the first wife he may, however, marry again the second wife." And again, "If, on being told of the death of his wife, he had married her sister, but being afterwards informed that she had been alive at the time [he had married the sister], but is now dead,
