John Wesley on Numbers 21:3

They utterly destroyed them - Neither Moses nor the whole body of the people did this but a select number sent out to punish that king and people, who were so fierce and malicious that they came out of their own country to fight with the Israelites in the wilderness; and these, when they had done this work, returned to their brethren into the wilderness. But why did they not all now go into Canaan, and pursue this victory? Because God would not permit it, there being several works yet to be done, other people must be conquered, the Israelites must be farther humbled and tried and purged, Moses must die, and then they shall enter, and that in a more glorious manner, even over Jordan, which shall be miraculously dried up, to give them passage. Hormah - That is, utter destruction.