“Why will you discourage the heart of the people of Israel from going over into the land that the LORD has given them?” (v7). When the Reubenites and others wanted to settle outside of Canaan (beyond the Jordan river, v5), and not join the other Israelites in conquering their land, Moses rebuked them. Their choice to sit out the battle would discourage everyone else, just as had occurred with the 12 spies (v8). Moses made them promise to join the battle for Canaan, and only then would they return to their own beyond-Jordan inheritance.
“Do what you have promised” (v24). Our love for God is expressed in how we treat each other: giving real support, fulfilling promises, and inspiring faith.