The request of the tribes of Gad and Reuben to settle on the eastern side of the Jordan River triggers a profound moral and national crisis. Moses immediately recognizes their petition as a severe threat to the solidarity of the Israelites and rebukes them for the inherent injustice of their demand. The primary approach among commentators is that Moses protests the inequity of one group claiming territory already conquered through the shared effort of the entire nation, leaving the rest of the people to continue risking their lives in battle [העמק דבר, מלבי"ם]. He expresses deep rhetorical astonishment at the very idea that they would let their brothers face danger alone [רש"י].
Moses carefully frames his rebuke by questioning whether the rest of the nation must merely arrive at the battlefield, deliberately avoiding language that implies actively fighting or eagerly marching out. This distinction carries multiple layers of meaning. First, while marching out to battle implies eagerness and a desire for combat, being brought to a war describes a situation of necessity where people are forced into danger against their will. Moses emphasizes that the other tribes would also prefer to rest and settle their land, but the war is forced upon them. Therefore, the attempt by the tribes of Gad and Reuben to evade this shared burden is especially jarring [ברכת אשר].
Furthermore, Moses addresses a hidden assumption made by these tribes that since God fights for Israel, human military effort is unnecessary. Moses agrees that God performs the miracles, but he clarifies that the Israelites are still obligated to physically show up, stand guard, and share in the physical burden. This is precisely why he speaks of arriving at the battlefield rather than engaging in actual combat [אור החיים, מלבי"ם].
When addressing the two tribes, Moses speaks to each separately, hinting at their distinct standings. The tribe of Gad is the only one that received an explicit blessing from Jacob for military success. Moses is baffled as to how the rest of the nation could go to war without the military vanguard that possesses the blessing of victory. On the other hand, the tribe of Reuben carries the weight of a past sin and lacks any specific military blessing, meaning they certainly have no special right to stay behind [שפתי כהן].
The greatest danger lies in the consequences of their actions. By choosing to settle peacefully to shepherd their flocks [ביאור שטיינזלץ], these tribes disconnect themselves from the collective, which could lead to a national disaster. Moses suspects their intention is to discourage the rest of the nation, or that this will be the inevitable result. If the strongest tribes, blessed with victory, refuse to cross the Jordan, the rest of the Israelites will despair and avoid entering the land altogether [ספורנו, שפתי כהן].
Such behavior threatens to repeat the disaster of the spies, potentially resulting in the nation being destroyed or forced to remain in the desert. This is a particularly tangible danger as Moses nears the end of his life, since he will no longer be there to perform the miracles needed to sustain a massive population in the wilderness [רלב"ג]. Finally, the very act of separating from the nation diminishes the shared collective merit. That collective strength was essential for the initial victories and the conquest of the very land these tribes now wish to inhabit [אור החיים].