1 Chronicles 5:1-26

Now in chapter five we get to the descendants of Reuben, who lost his birthright. It was given to the sons of Joseph, the son of Israel.

And so his genealogy is not reckoned after the birthright (1 Chronicles 5:1).

That genealogy after the birthright, of course, will come to Joseph.

But Judah prevailed above his brothers, and of him came the chief ruler or David; but the birthright was Joseph's (1 Chronicles 5:2):

So even though the birthright was Joseph, the leadership was to come from Judah, and ultimately from Judah is to come Jesus Christ.
Now in verse nine, we read concerning the tribe of Reuben.

That they went east and inhabited the entering of the wilderness from the river Euphrates: because their cattle were multiplied in the land of Gilead (1 Chronicles 5:9).

And so they went over to what is present-day Iraq, as far as Iraq, and they dwelt in that area. And so the tribe of Reuben and then next to the tribe of Gad, these are the tribes that settled on the east bank of the Jordan River. And then after them, the half the tribe of Manasseh, and it gives the names of some of those from the half the tribe of Manasseh, those all that dwelt on the other side.
But in verse twenty-five concerning the tribe of Reuben and Gad and half the tribe of Manasseh.

They transgressed against the God of their fathers, and they went a whoring after the gods of the people of the land, whom God destroyed before them. And the God of Israel stirred up the spirit of Pul the king of Assyria, and the spirit of Tilgathpilneser the king of Assyria, and he carried them away, even the Reubenites, the Gadites, and half the tribe of Manasseh, and brought them unto Halah, unto Habor, and Hara, and to the river Gozan, unto this day (1 Chronicles 5:25-26).

And so, they were the first to fall. Those tribes that settled on the east bank of the Jordan River. And the reason for their fall is their transgression against the God of their fathers and their beginning to worship other gods. "