Numbers 32:1-19

Maybe the leaders of Reuben and Gad concluded that their brethren could easily handle the remaining Canaanites without their help. The Israelites had defeated the Midianites and earlier Sihon and Og easily. Also the pastures of Gilead attracted them. Their request revealed a selfish desire that would have cost their brethren dearly. The remaining tribes would have had to fight their battles without Reuben and Gad’s help.

"In Numbers 32:1 the sons of Reuben are mentioned before the sons of Gad, but in subsequent references this order is reversed. The reason is very likely that the tribe of Gad was more important than that of Reuben [cf. Genesis 49:4]. There is an oblique confirmation of this supposition on a stone that King Mesha of Moab set up around 850 B.C., following his defeat of the Israelites [i.e., the Moabite Stone]. This stone bears an inscription that refers to Gad as a people that lived there from times immemorial." [Note: Maarsingh, p. 110.]

Moses saw this request as potentially very discouraging to the other tribes and warned Reuben and Gad against disheartening their brothers.