Comentario sobre Génesis 4:19

ויקח לו למך AND LAMECH TOOK UNTO HIMSELF — It would not have been necessary to state all this in detail except to inform us by the conclusion of the narrative that the Holy One, blessed be He, kept the promise He made when He said, שבעתים יקם קין “vengeance shall be taken of Cain after seven generations״; for Lamech arose after he had begotten children and had raised the seventh generation and killed Cain. It is to this that the statement refers: כי איש הרגתי לפצעי וגו “for I have slain a man to my wounding etc.” (v. 23).

Lemech married two women. Adah, whom he married to bear children, gave birth to two righteous men, one a shepherd like many of the righteous, and one the inventor of instruments for praising Hashem. But Tzillah, whom he married for pleasure, gave birth to a weapon maker in the spirit of Kayin.

ויקח לו למך, it appears that the generations prior to Lemech and even subsequent to him did not marry more than one wife. Lemech, who was the first one to marry two wives, was also the first one of whom disagreements between him and his wives have been recorded. The two wives were jealous one of the other so that Lemech had to scare them that he would kill them if they would disturb his domestic peace.