The first thing the two-and-a-half tribes do once they settle back on the East side of the Jordan is build an altar — exactly as God had expressly forbidden. The other Israelites should “smite the inhabitants of that city with the edge of the sword, destroying it utterly, and all that is therein, and the cattle thereof, with the edge of the sword.” (Deuteronomy 13:15 KJV)
Fortunately for everyone, they send a delegation to ask about it, and the Eastern tribes say that it’s not an altar, really, but a reminder of the one true altar, and if the Lord doesn’t like it, He should strike them down.
The rules are arbitrary and capricious. The Lord kills Nadab and Abihu, Aaron’s sons, because “they offered strange fire before the Lord, which He commanded them not.” (Leviticus 10:1) but two-and-a-half tribes build a strictly forbidden altar, and that’s okay. It doesn’t make sense.
What does make sense is just how terrified the other Israelites are. They know just how petty and mean their God is, and how He takes out His anger on everyone. They are still being punished for the orgies their grandparents had back in Acacia.
In the end, the Israelites renew their vows to the Lord, and Joshua dies. It was a quick book.
Next: Judges 1-2