2 And Israel voweth a vow to Jehovah, and saith, 'If Thou dost certainly give this people into my hand, then I have devoted their cities;'

Matthew Henry's Commentary on Numbers 21:2

Commentary on Numbers 21:1-3

(Read Numbers 21:1-3)

Before the people began their march round the country of Edom, the king of Arad, a Canaanite, who inhabited the southern part of the country, attacked them in the wilderness, and took some prisoners. This was to lead the Israelites to look more thoroughly to the Lord.