Комментарий к Берешит 25:19

ואלה תולדות יצחק AND THESE ARE THE PROGENY OF ISAAC — viz, Jacob and Esau who are spoken of in this section.

AND THESE ARE THE GENERATIONS OF ISAAC, ABRAHAM’s SON. Scripture says this of Esau and Jacob,¹Ramban’s intent is to teach us that the word toldoth is not to be understood in the broad sense of “generations” but in the more specific sense of “children.” Thus the verse reads, And these are the children of Isaac, namely, Esau and Jacob mentioned further on. Compare Ramban at beginning of Seder Noach. Isaac’s sons who are mentioned further on. Scripture further mentions the circumstances of their birth.²Thus, in order to explain fully the story of Jacob and Esau, Scripture begins with an account of their genealogy.

אברהם הוליד את יצחק, according to the plain meaning of the text this statement was necessary to prevent the wrong impression being created by the previous statement in verse 12 where Ishmael is described merely as having been born by Hagar the Egyptian woman. Here when Avraham’s principal son, Yitzchok is the subject of the paragraph, it was important to repeat who had fathered him. He was the son of Avraham’s true wife, his lifetime companion, and G’d had predicted in Genesis 21,12 that Avraham’s descendants would always be known through his son Yitzchok and his descendants. We have a similar verse in Chronicles I 1,28 describing Yitzchok and Ishmael as Avraham’s sons, [but not in the chronological order of their births, to remind us that the principle of preference for the firstborn was ignored. Ed.] In connection with the sons of Keturah, described as the concubine of Avraham, Chronicles does not even spell out that Avraham fathered Keturah’s sons. In fact, in verse 34 of that chapter in Chronicles, the fact that Avraham fathered Yitzchok is repeated once more, no such repetition being made concerning Ishmael.