במדבר, פרק ל״ב, פסוק י״ח

The tribes of Gad and Reuben stand before their brothers with a firm declaration of loyalty, promising to remain by their side throughout the long process of settling the land. Their commitment goes far beyond a simple military alliance. While they will serve as the armed vanguard during the initial conquest, their duty does not end when the battles cease. Even after the wars are over and there is no longer a need to carry weapons, they vow not to return to their families [מלבי״ם]. This pledge is absolute, meant to ensure that not a single individual among them will go back to his private home across the Jordan River [אוהב גר].

This extended commitment to stay long after the fighting stops is meant to prevent any feelings of unfairness or resentment from the rest of the nation. The tribes that settled across the Jordan have already secured their defined territories and could easily return to them. In contrast, the rest of the Israelites are entirely unable to establish their own homes until the entire land is formally distributed [העמק דבר]. Recognizing this difference, Gad and Reuben promise to wait and assist until every single tribe has fully received its portion. They will not depart until both the military conquest and the final division of the land of Canaan are completely finished [ביאור שטיינזלץ, העמק דבר, מלבי״ם].