Genesis 26:34

34.And Esau was forty years old. For many reasons Moses relates the marriages of Esau. Inasmuch as he mingled himself with the inhabitants of the land, from whom the holy race of Abraham was separated, and contracted affinities by which he became entangled; this was a kind of prelude of his rejection. It happened also, by the wonderful counsel of God, that these daughters-in-law were grievous and troublesome to the holy patriarch (Isaac) and his wife, in order that they might not by degrees become favorable to that reprobate people. If the manners of the people had been pleasing, and they had had good and obedient daughters, perhaps also, with their consent, Isaac might have taken a wife from among them. But it was not lawful for those to be bound together in marriage, whom God designed to be perpetual enemies. For how would the inheritance of the land be secured to the posterity of Abraham, but by the destruction of those among whom he sojourned for a time? Therefore God cuts off all inducements to these inauspicious marriages, that the disunion which he had established might remain. It appears hence, with what perpetual affection Esau was loved by Isaac; for although the holy man justly regarded his son’s wives with aversion, and his mind was exasperated against them, he never failed to act with the greatest kindness towards his son, as we shall afterwards see. We have elsewhere spoken concerning polygamy. This corruption had so far prevailed in every direction among many people, that the custom, though vicious, had acquired the force of law. It is not, therefore, surprising that a man addicted to the flesh indulged his appetite by taking two wives.