What does Deuteronomy 3:15 mean?

This land we took in possession at that time: from Aroer, which is by the valley of the Arnon, and half the hill country of Gilead, and its cities, I gave to the Reubenites and to the Gadites:

and the rest of Gilead, and all Bashan, the kingdom of Og, I gave to the half-tribe of Manasseh; all the region of Argob, even all Bashan. (The same is called the land of Rephaim.

Jair the son of Manasseh took all the region of Argob, to the border of the Geshurites and the Maacathites, and called them, even Bashan, after his own name, Havvoth Jair, to this day.)

To the Reubenites and to the Gadites I gave from Gilead even to the valley of the Arnon, the middle of the valley, and its border, even to the river Jabbok, which is the border of the children of Ammon;

the Arabah also, and the Jordan and its border, from Chinnereth even to the sea of the Arabah, the Salt Sea, under the slopes of Pisgah eastward.

I commanded you at that time, saying, “Yahweh your God has given you this land to possess it. You shall pass over armed before your brothers the children of Israel, all the men of valor.