v1-3: The Canaanite king of Arad attacked Israel. They were thus right to destroy them. This thorough dealing with an ungodly people pictures what should be our attitude to dealing with personal sins. The Lord honoured the prayers of the people to this end.
v4-5: Having won a decisive victory, the people grew impatient and again grumbled. It seems that everything about their lives became a reason for complaining; they despised God's provision and protection.
v6: A different punishment, as the Lord sent snakes among them. They had been protected from snakes for nearly 40 years.
v7: Only when they began to suffer did the people realise their sins. We need a more sensitive conscience that recognises personal sin early.
v8-9: The Lord's answer. He could simply have taken away the snakes (compare Ex 15.22-17.7, where God provided pure water, manna and quail); but instead He challenged the people to exercise faith, to believe His word and to depend upon His remedy (see 16.47-48). We are pointed to Christ, whom God provided as the propitiation for our sins (John 3.14-15). 'Here a divine remedy was provided against a national calamity; a sovereign antidote against spreading and moral poison.' (John Fawcett, Christ Precious)
v10-20: The continuing journey toward the land of the Amorites.
v16-18: Blessing gained by effort; they was water because of the work of the leaders. They set an example. (Perhaps the people were unwilling to help.) Scripture does not commend idleness.
v17-18: A song; the first since the crossing of the Red Sea (Ex 15); after the wanderings, without rejoicing, we enter a period largely of victories, although with some difficulties. The Lord takes us through 'seasons', and we are to be faithful whatever He takes us through.
v21-22: As with Edom, Israel sent a message that they would travel through the land on the king's highway.
v23-25: Israel defeated the Amorites, who also had attacked them. They dwelt in their cities. This was not the promised land, although Reuben, Gad, and half of the people of Manasseh chose to live here. This was a 'second best'.
v27-29: See Jer 48.43-46; a later repetition of this defeat.
v31: Israel settled in the land taken from the Amorites; but this was not the promised land. Perhaps their period here influenced those tribes that later wanted to stay here, east of the Jordan.
v32-35: The army of Og, king of Bashan, was totally destroyed also. This pattern of decisive victories should have continued once Israel entered the promised land, however they failed to fully rid the land of Canaanites.