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בשכן ישראל בארץ ההוא WHEN ISRAEL DWELT IN THAT LAND — before he came to Isaac at Hebron, all these troubles happened to him.

AND ISRAEL HEARD OF IT. Scripture relates Jacob’s humility. He heard that his son had profaned his couch, but yet he did not command them to remove him from his house and from inclusion among his sons so that he should not inherit with them. Instead, he is counted among them, as it is written, And the sons of Jacob, were twelve, and he is counted first. It is for this reason that Scripture has combined the two sections of the Torah²³⁶In the written Torah the upper section concludes with the words, And Israel heard of it. Then a new section begins, And the sons of Jacob were twelve. Ramban explains why the Masorah combines them into one verse. through one verse. For although this is the beginning of a subject wherein Scripture commences to count the tribes now that they were all born, it hints that Reuben was not rejected on account of his deed.
In line with the simple meaning of Scripture it is possible that Reuben disturbed the couch of Bilhah [Rachel’s handmaid] because he feared that she might give birth again from Jacob, for he, being the first-born and thinking of taking two portions of the inheritance, would thus lose more than all the brothers. He had no fear of his mother for she was elderly. Zilpah had perhaps died, or it may be that he had concern for his mother’s honor, and since Zilpah was her handmaid, he did not disturb her. It was for this reason that the right of the first-born was taken away from Reuben, measure for measure. And this is the purport of the verse, And the sons of Jacob were twelve, meaning that he did not beget children after that.

וישמע ישראל, this matter has been reported only so that we can understand why Yaakov passed over his firstborn son Reuven when in his blessings before his death he referred to him as פחז כמים אל תותר כי עלית על משכבי אביך (49,4). “the one who was as unrestrained as water when you mounted the bed of your father, does not deserve the privileges associated with the birthright.” [These privileges were allocated by Yaakov in part to Yehudah, commencing with the reign of David, and in part to Joseph, as the firstborn son of Rachel. The latter was accorded two tribal heads, (Ephrayim and Menashe) among the twelve tribes. Ed.]