Verses 1-5 – The tribes that settled on the eastern side of the Jordan River (Reuben, Gad, and half of Manasseh) had asked for the land from Moses after they helped Joshua conquer the land on the river’s western side. Reuben lost the honor of the firstborn, a double portion of inheritance, when he defiled his father’s bed with one of Jacob’s concubines Bilha.
Verses 9, 10 – Reuben’s earlier successes had allowed this tribe to stretch all the way to the Euphrates River and to defeat the Hagrites. These were the Ishmaelites, the descendants of Hagar.
Verses 18-22 – The armies of Reuben, Gad and Manasseh succeeded in battle because they trusted God. Although they had instinct and skill as soldiers, they prayed and sought God’s direction. When we trust in our own cleverness, skill, and strength rather than in God, we open the door for pride. Psalm 20:7 says, “Some trust in chariots and some in horses, but we trust in the name of the Lord our God.”
Verse 22 – The exile mentioned here refers to the exile of the ten northern tribes to Assyria in 722 B.C. These tribes never returned to their homeland (2 Kings 15:29-17:41).
Verse 23 – There was no tribe of Joseph. Instead, Joseph’s sons became the ancestors of two separate tribes, Ephraim and Manasseh. The tribe of Manasseh occupied territory on both sides of the Jordan River.
Verse 25 – Even though this part of the tribe of Manasseh contained some outstanding people, they deviated from God and adopted the idolatry of the nations around them.
Verse 26 – This passage leaves no doubt that this happened because of their idolatry.