“Let us now build an altar, not for burnt offering, nor for sacrifice, but to be a witness between us and you” (v26-27). Most of Israel’s tribes settled west of the Jordan River, while a few settled east. When the eastern tribes built an “imposing altar” on their land, it seemed to be an act of religious rebellion. When the western tribes got ready for battle (v12), the easterners quickly affirmed their loyalty, explaining that the altar symbolized their unity with all Israel.
The unity of God’s people was not language or ethnicity, but the commitment to worship God together: “to walk in all his ways … to serve him with all your heart" (v5).