Bible Commentaries
Numbers 21

Verses 1-20

The long detour (20:14-21:20)

A well used trade route called the King’s Highway ran from Ezion-geber on the Red Sea through the kingdoms of Edom and Moab into Syria. Moses decided to use this route for Israel’s entrance into Canaan. He therefore asked the Edomite king for permission to pass through his territory, promising not to damage Edom’s fields or use its water. If, in an emergency, the Israelites needed to use Edom’s water, they would pay for it. Moses expected a favourable reply, because Israel and Edom were brother nations (Edom being descended from Esau, Israel from Jacob), but the king of Edom refused (14-21).
Israel changed route and soon came to Mount Hor. There Aaron died, his death being God’s judgment for his sin at Meribah. God announced his death in advance, so that a ceremony could be held to appoint Eleazar, Aaron’s oldest surviving son, as the replacement high priest before Aaron died (22-29).

When one of the Canaanite kings heard that Israel was heading towards Canaan, he launched an attack and took some of the people captive. Israel responded promptly, and with God’s help destroyed the attackers. It was the first step towards Israel’s conquest of Canaan (21:1-3; cf. Deuteronomy 20:16-18).

The long detour that the Edomites forced upon the Israelites caused the people to become impatient and complaining again. God punished them with a plague of snakes whose bite produced burning pains and even death. Moses prayed for the people, and God replied by promising to heal all who stopped complaining and trusted in him (4-9).
Moving forward again, the Israelites journeyed around the fortified areas of Moab, crossed the Zered River, and headed north across the tableland region east of the Dead Sea. The writer mentions two significant events in the brief account of the journey across the tableland. One was the crossing of the Arnon River, which marked the boundary between Moabite and Amorite territory; the other was the discovery of water in one particularly dry region. The people celebrated the events by singing well known songs (10-20).

Verses 21-35

Territory seized east of Jordan (21:21-22:1)

Although Israel had not attacked its brother nation Edom when the king of Edom refused a request to pass through his territory, it did not hesitate to go to war with the Amorite king Sihon who refused a similar request. The Amorites started the fighting, but Israel crushed their army, conquered their chief city Heshbon, and overran their territory (21-25). The victory was especially pleasing to Israel, because the Amorites had only recently gained this territory from the Moabites. The Amorites had written a victory song to celebrate their conquest of Moab (along with its national god Chemosh), but now they themselves were conquered (26-30). As a result of this victory, Israel now controlled an area on Canaan’s eastern border that extended from the Arnon River north to the Jabbok River (31-32).
Israel expanded even farther north with its conquest of Og, another Amorite king, who ruled over the rich pasture land of Bashan. This gave Israel control of the whole region east of the Jordan River (33-35). The Israelites set up their main camp on the plains of Moab, east of Jordan opposite Jericho (22:1).