Comentario sobre Deuteronómio 25:6

והיה הבכור AND IT SHALL BE THE FIRSTBORN … — It is the eldest brother who is to perform the duty of levirate marriage (Sifrei Devarim 289:1; Yevamot 24a).

AND IT SHALL BE THAT THE FIRSTBORN THAT SHE BEARETH SHALL SUCCEED IN THE NAME OF HIS BROTHER THAT IS DEAD. It [the true purport thereof] is not the simple meaning that they call the first son by the name of the dead, Reuben or Shimon as his name was, for in the case of Boaz it says thus, that the name of the dead be not cut off from among his brethren,³⁷⁶Ruth 4:10. and yet they did not call the child born [to Boaz and Ruth] Machlon. But this verse by way of the Truth, [the mystic teaching of the Cabala], is an assurance³⁷⁷See Vol. I, p. 469, Note 155, and p. 470, Note 163. and thus it is to be understood in its simple sense. And our Rabbis found support in this verse for the following laws:³⁷⁸Yebamoth 24a. that the eldest [surviving] brother contracts the levirate marriage, that a sterile woman may not be contracted for such marriage, nor the wife of a eunuch since his name was “blotted out” [when he was yet alive]. Now, all these are but Scriptural supports [for laws of levirate marriage], because the laws of the sterile widow and the widow of the eunuch are derived from the very essence of the Scriptural section [and are not derived from the Scriptural supports quoted].³⁷⁹That is to say, since the purpose of the levirate marriage is as stated by Scripture that the name of the dead be not blotted out from Israel by definition, a sterile woman is excluded from the commandment for she cannot fulfill that function. No special verse is needed to exclude her from such a marriage. Similarly the widow of the eunuch may not be contracted for such a marriage since his name was already “blotted out” when yet alive and no special verse is necessary to exclude his widow from such a marriage. These laws, therefore, are derived from the very essence of the chapter, and the Rabbis merely found support for them in the language of the quoted verse.

ולא ימחה שמו מישראל, in that the child born from this union will be considered by G’d as if the deceased had fulfilled the commandment to be fruitful. This is easily understood when we consider that this child is the product of a legal marriage entered into by the deceased husband of his mother. The fact that the deceased’s brother did not have to go through a marriage ceremony with the widow of his brother makes this clear to everyone. This explains why G’d would be angry at the brother who refuses to marry his sister-in-law, as he thereby deprived his deceased brother forever from fulfilling the mitzvah of being fruitful