Commentary on the Bible, by Adam Clarke, [1831], at sacred-texts.com
The genealogies of Reuben, Ch1 5:1-10. Of Gad, Ch1 5:11-17. The exploits of Reuben, Gad, and the half tribe of Manasseh, Ch1 5:18-22. The genealogy of the half tribe of Manasseh, Ch1 5:23, Ch1 5:24. The idolatry of these tribes and their captivity by the Assyrians, Ch1 5:25, Ch1 5:26.
The sons of Reuben the first-born - As Reuben was the eldest son of Jacob, why was not his genealogy reviewed first? This verse answers the question; he lost the birth-right because of the transgression mentioned Gen 35:22; Gen 49:4, and the precedency was given to Judah; from him therefore came the chief ruler. This appears to be the meaning of the place.
And of him came the chief ruler - This is, by both the Syriac and Arabic, understood of Christ: "From Judah the King Messiah shall proceed." The Chaldee paraphrases the verse thus: "Seeing Judah prevailed over his brethren, so the kingdom was taken from Reuben and given to Judah; and because he was strong, so was his kingdom. Levi also was godly, and did not transgress in the matter of the golden calf; therefore the high priesthood was taken away from the children of Reuben, and on their account from all the first-born, and given to Aaron and his sons. The custody of the sanctuary belonged to the Levites, but the birthright to Joseph." - T.
Beerah his son - After their separation from the house of David the ten tribes continued to have princes of the tribes; and this continued till the time that Tiglath-pileser carried them captives into Assyria. At that time Beerah was their prince or chief; and with him this species of dominion or precedency terminated. According to the Targum, Beerah was the same as Baruch the prophet.
Who dwelt in Aroer - This town was situated on the river Arnon; and Nebo was both a city and a mountain in the same country. They both lay on the other side of Jordan.
And they dwelt in their tents - The Hagarites were tribes of Nomade, or Scenite, Arabs; people who lived in tents, without any fixed dwellings, and whose property consisted in cattle. The descendants of Reuben extirpated these Hagarites, seized on their property and their tents, and dwelt in their place.
Joel the chief - "Joel, prince of the Sanhedrin; and Shapham, master of the college; and Jaanai and Shaphat, judges in Mathnan." - T.
And their brethren - This verse is wanting both in the Syriac and in the Arabic.
The suburbs of Sharon - There were three places of this name: that mentioned here was a district in the country of Bashan beyond Jordan, (see Jos 12:18); there was another that lay between Caesarea of Palestine and Joppa; and there was a third between Mount Tabor and the Sea of Tiberias. See Calmet.
They made war with the Hagarites - This is probably the same war that is mentioned Ch1 5:10. Those called Hagarites in the text are everywhere denominated by the Targum הונגראיי Hongaraai, Hongarites.
They put their trust in him - Or, as the Targum says, "Because they trusted במימריה bemeymriah, in his Word."
They took away their cattle - This was a war of extermination as to the political state of the people, which nothing could justify but an especial direction of God; and this he could never give against any, unless the cup of their iniquity had been full. The Hagarites were full of idolatry: see Ch1 5:25.
For there fell down many slain - The hundred thousand men mentioned above were probably made slaves, and were not slain. The Targum says, one hundred thousand souls of men.
The war was of God - The Targum says, the war was מן מימרא דיי min meymera dayai, "from the Word of the Lord."
The gods of the people of the land - We see the reason why God delivered the Hagarites into the hands of these tribes; they were abominable idolaters, and therefore God destroyed them.
Tilgath-pilneser - Many MSS. have תגלת Tiglath instead of תלגת Tilgath. The Syriac, the Septuagint, and the Chaldee, have the same reading as in Kg2 15:29, etc.
Brought them unto Halah - See the notes on Kg2 17:6 (note), and Kg2 18:11 (note), for many particulars of these wars, and consequent captivity. It is a pity that some method were not found out to harmonize the books of Kings with the books of Chronicles, that the variations might be seen at one view.