Deuteronomy 33:6

“Let Reuben live, and not die--Although deprived of the honor and privileges of primogeniture, he was still to hold rank as one of the tribes of Israel. He was more numerous than several other tribes (Num 1:21; Num 2:11). Yet gradually he sank into a mere nomadic tribe, which had enough to do merely "to live and not die." Many eminent biblical scholars, resting on the most ancient and approved manuscripts of the Septuagint, consider the latter clause as referring to Simeon; "and Simeon, let his men be few," a reading of the text which is in harmony with other statements of Scripture respecting this tribe (Num 25:6-14; Num 1:23; Num 26:14; Jos 19:1).”

“Let not his men be few - literally, “a number,” i. e., “a small number,” such as could be easily counted (compare Genesis 34:30 note). While the verse promises that the tribe shall endure and prosper, yet it is so worded as to carry with it a warning. The Reubenites, occupied with their herds and flocks, appear, soon after the days of Joshua, to have lost their early energy, until in later times its numbers, even when counted with the Gadites and the half of Manasseh, were fewer than that of the Reubenites alone at the census of Numbers 1:0 (Compare 1 Chronicles 5:18 with Numbers 1:20.) No judge, prophet, or national hero arose out of this tribe. The tribe of Simeon, which would according to…”

“Let Reuben live - Though Reuben deserve to be cut off or greatly diminished and obscured, according to Jacob's prediction, Gen 49:4, yet God will spare them and give them a name and portion among the tribes of Israel, and bless them with increase of their numbers. All the ancient paraphrasts refer this to the other world, so far were they from expecting temporal blessings only. Let Reuben live in life eternal, says Onkelos, and not die the second death. Let Reuben live in this world, so Jonathan and the Jerusalem Targum, and not die that death which the wicked die in the world to come. Deuteronomy 33:7”

“33:6 Moses said this about the tribe of Reuben: The NLT adds this line for clarity (cp. 33:7, 8, 12, etc.). • Reuben was Jacob’s eldest son by Leah (see Gen 29:32). His sin against his father (Gen 35:22) might explain his tribe’s lack of prominence (Gen 49:3-4).”

“Gen 49:3, Gen 49:4, Gen 49:8; Num 32:31, Num 32:32; Jos 22:1-9 Deuteronomy 33:7”

“The blessings upon the tribes commence with this verse. "Let Reuben live and not die, and there be a (small) number of his men." The rights of the first-born had been withheld from Reuben in the blessing of Jacob ( Gen 49:3); Moses, however, promises this tribe continuance and prosperity. The words, "and let his men become a number," have been explained in very different ways. מספּר in this connection cannot mean a large number (πολὺς ἐν ἀριθμῷ, lxx), but, like מספּר מתי ( Deu 4:27; Gen 34:30; Jer 44:28), simply a small number, that could easily be counted (cf. Deu 28:62). The negation must be carried on to the last clause. This the language will allow, as the rule that a negation can…”