Now there were with us seven brethren
That is, there was in the city, town or neighbourhood, where these Sadducees dwelt, probably at Jerusalem, a family, in which were seven sons, all brethren by the father's side; for brethren by the mother's side were not counted brethren, nor obliged by this law F1; whether this was a reigned case which is here and in the following verses put, or whether it was real fact, which is possible, it matters not: and the first, when he had married a wife, deceased, and having no issue, left his wife unto his brother: the eldest of these seven brethren married a wife, and after some time died, having no children, son or daughter, by his wife; and therefore, according to the above law, leaves her to his next brother to marry her, and raise up seed unto him; which, according to the Jewish canons F2, could not be done before ninety days, or three months after the decease of his brother; for so long they were to wait and see, whether she was with child by his brother or not; for if she was, it was not necessary, yea, it was unlawful for him to marry her.
F1 Maimon. Hilch. Yebum, c. 1. sect. 7.
F2 T. Bab. Erubin, fol. 47. 1. Maimon. ib. c. 1. sect. 19.