Summary: Following the division of the land between all of the tribes, Joshua summons the tribes of Reuben, Gad and half of the tribe of Menashe who chose to settle on the eastern side of the Jordan River.
In his final days Joshua assembles the people and encourages them to remain steadfast in their connection to God, or else forfeit His Divine support. In his final speech before his death, Joshua retraces the whole of Jewish history and concludes by entreating the people to abandon idolatry and direct their hearts to God. The book ends with the deaths of Joshua and Elazar the son of Aharon, and the burial of Joseph.
A deeper look: In an act of apparent treachery the eastern tribes built an altar near the Jordan River. Since the tabernacle had been established in Shiloh, it was forbidden to offer sacrifices anywhere else, even to God as there was a concern that it could lead to idol worship. As the western tribes readied themselves to do battle, Pinchas ben Elazar was sent with ten emissaries to elicit an explanation. Pinchas commanded this mission as he had led the fight against the Midianite idol worship of Baal Peor when killing Zimri and Cozbi (Numbers 25:7-14).
The eastern tribes explained that the altar was not meant for offerings but was merely symbolic to show the future generations that all of the tribes – even those on the eastern side of the Jordan – had a share in God. After the true intent is related to the other tribes, approval was given and the altar was named eid – meaning witness.
Rabbi Avraham Yitzchak Sorotzkin explains the deeper nature of the perceived threat by citing Rabbi Yehudah Löwe ben Bezalel (known as the Maharal, d. 1609) who explained that the unity of the Jewish people derives it source from the Mishkan (Tabernacle) and subsequently, the Beit HaMikdash (Rinat Yitzchak on Joshua 22:19). Without unity, the Shechinah (Divine Presence) cannot rest on the people.
This is the final message of the book of Joshua. Our unity is dependent on our connection with God and in turn, when we find unity His Presence rests with us. With this in mind, we will continue next week with the Book of Judges.