Charles Ellicott Commentary Deuteronomy 33:6

"Let Reuben live, and not die; Nor let his men be few." — Deuteronomy 33:6 (ASV)

Let Reuben live, and not die. —“‘Live’ in this world,” says Rashi, “and ‘not die’ in the world to come.” The prayer meant that his misdeed (Genesis 35:22) should not be remembered. Rashi also notices the juxtaposition of this record with the sentence, the sons of Jacob were twelve. Reuben was not cut off, but he was disinherited (1 Chronicles 5:1), and his father’s blessing had so much disapproval in it that Moses’ prayer for him was not unnecessary.

And let not his men be few. —The sentence is difficult. The Septuagint inserts Simeon, “Let Simeon be many in number.” But there is no need for this. The most terrible destruction ever wrought in Israel by the word of Moses came upon Dathan and Abiram (who were Reubenites), when they and all that appertained to them went down alive into the pit. We cannot say how far the tribe was diminished by this terrible visitation and the plague that followed (Numbers 16). The fighting men of the tribe, however, had slightly decreased in the second census (Numbers 1:21; Numbers 26:7), and at this time, only two of all the twelve tribes had a smaller force than Reuben.

It seems best, therefore, to take the whole verse as applying to Reuben, and the negative in the first clause as covering the second clause also. “Let not his men be a (small) number.” The omission of Simeon may be accounted for by his coming within the inheritance of Judah, in Canaan, and enjoying the blessing and protection of that most distinguished tribe. Rashi also takes this view.