This account fits chronologically after Numbers 21:13. It records two great victories that God gave His people over two of the mighty Amorite kings. [source][source][source]
"The term Amorite has various meanings in the OT: Canaanites generally (e.g, Genesis 15:16), inhabitants of the land west of the Jordan (e.g, Joshua 5:1), inhabitants of the regions of Judah (e.g, Joshua 10:5-6), inhabitants of the Negeb and the region to the southeast of the Dead Sea (e.g, Genesis 14:7), and very often, as here, the inhabitants east of the Jordan under the rule of Sihon and Og ..." [1][source]
Moses made his peaceful request for permission to pass through Sihon"s territory and into the Promised Land ( Numbers 21:22) realizing that Sihon would not allow this (cf. Deuteronomy 2:24-26). Compare Moses" request that Pharaoh would let the Israelites go in Exodus 5:1 (cf. Exodus 3:19). [source][source][source]
". . . this was done simply to leave the decision of his fate in his own hand ..." [2][source]
Sihon then attacked Israel ( Numbers 21:23), but Israel defeated his army ( Numbers 21:24). Moses had very little to do with the acquisition of any land for Israel. [3] This victory gave the Israelites possession of all of Sihon"s territory. It extended south to the Arnon and north to the Jabbok, which flows into the Jordan River from the east about halfway between the Sea of Chinnereth (Galilee) and the Dead Sea. It included Jazer, a town that the Israelites defeated ( Numbers 21:32). This victory over one of the most powerful of the Canaanite city-states, Heshbon, inspired poets in Israel who wrote proverbs ( Numbers 21:27) to compose songs commemorating God"s deliverance ( Numbers 21:27-30). [source][source][source]
"The summons to come to Heshbon and build this ruined city again [4], was not addressed to the Israelites, but to the conquered Amorites, and is to be interpreted as ironical ..." [5][source]
Chemosh ( Numbers 21:29) was the chief Moabite deity and was similar to the Ammonite god Molech (cf. Judges 11:24; 1 Kings 11:7). [4] See Deuteronomy 2:16-37 for another account of this victory. John Van Seters argued that Numbers 21:21-25 derives from conflation of Deuteronomy 2:26-37 and Judges 11:19-26. [7] John R. Bartlett countered that the Numbers passage is the source of the other two accounts. [8][source]