ספר בראשית

Genesis 49,4. “unstable as water, you will not enjoy ‎the additional portion due to the firstborn;” How could ‎Yaakov deliberately ignore the commandment not to deprive ‎even the son of a wife who was hated of the rights accruing to ‎him as a firstborn? (Deut. 21,17) Nachmanides writes concerning ‎this problem that Yaakov penalized Reuven in accordance with ‎the nature of his sin. Personally, I believe that Yaakov saw in his prophetic ‎vision of the future what the Torah calls ‎גוי וקהל גויים‎, “a nation ‎and a community of nations,” (Genesis 35,11) a promise made to ‎him by G’d at a time when he personally had concluded siring ‎children, that another two tribes would become part of the Jewish ‎people, so that in order for the number of tribes not to exceed ‎the number 12, “something had to give.” He had not been aware ‎that these two “tribes” would not be sons, but grandsons of his. ‎The only way he was able to explain G’d’s promise of two more ‎tribes was by assuming that an existing one would prove ‎unworthy.‎