And Israel vowed a vow unto the LORD, and said, If thou wilt indeed deliver this people into my hand, then I will utterly destroy their cities.

Wesley's Notes

21:2 I will utterly destroy them - I will reserve no person or thing for my own use, but devote them all to total destruction.

Jamieson-Fausset-Brown Bible Commentary

2, 3. Israel vowed a vow unto the Lord-Made to feel their own weakness, they implored the aid of Heaven, and, in anticipation of it, devoted the cities of this king to future destruction. The nature and consequence of such anathemas are described (Le 27:1-34; De 13:1-18). This vow of extermination against Arad [Nu 21:2] gave name to the place Hormah (slaughter and destruction) though it was not accomplished till after the passage of the Jordan. Others think Hormah the name of a town mentioned (Jos 12:14).

Matthew Henry's Concise Commentary

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.

Matthew Henry's Whole Bible Commentary

Chapter 21

The armies of Israel now begin to emerge out of the wilderness, and to come into a land inhabited, to enter upon action, and take possession of the frontiers of the land of promise. A glorious campaign this chapter gives us the history of, especially in the latter part of it. Here is, I. The defeat of Arad the Canaanite (v. 1-3). II. The chastisement of the people with fiery serpents for their murmurings, and the relief granted them upon their submission by a brazen serpent (v. 4-9). III. Several marches forward, and some occurrences by the way (v. 10-20). IV. The celebrated conquest of Sihon king of the Amorites (v. 21-32), and of Og king of Bashan (v. 33-35), and possession taken of their land.

Verses 1-3

Here is, 1. The descent which Arad the Canaanite made upon the camp of Israel, hearing that they came by the way of the spies; for, though the spies which Moses had sent thirty-eight years before then passed and repassed unobserved, yet their coming, and their errand, it is likely, were afterwards known to the Canaanites, gave them an alarm, and induced them to keep an eye upon Israel and get intelligence of all their motions. Now, when they understood that they were facing about towards Canaan, this Arad, thinking it policy to keep the war at a distance, made an onset upon them and fought with them. But it proved that he meddled to his own hurt; had he sat still, his people might have been last destroyed of all the Canaanites, but now they were the first. Thus those that are overmuch wicked die before their time, Eccl. 7:17. 2. His success at first in this attempt. His advance-guards picked up some straggling Israelites, and took them prisoners, v. 1. This, no doubt, puffed him up, and he began to thin that he should have the honour of crushing this formidable body, and saving his country from the ruin which it threatened. It was likewise a trial to the faith of the Israelites and a check to them for their distrusts and discontents. 3. Israel's humble address to God upon this occasion, v. 2. It was a temptation to them to murmur as their fathers did, and to despair of getting possession of Canaan; but God, who thus tried them by his providence, enabled them by his grace to quit themselves well in the trial, and to trust in him for relief against this fierce and powerful assailant. They, by their elders, in prayer for success, vowed a vow. Noe, When we are desiring and expecting mercy from God we should bind our souls with a bond that we will faithfully do our duty to him, particularly that we will honour him with the mercy we are in the pursuit of. Thus Israel here promised to destroy the cities of these Canaanites, as devoted to God, and not to take the spoil of them to their own use. If God would give them victory, he should have all the praise, and they would not make a gain of it to themselves. When we are in this frame we are prepared to receive mercy. 4. The victory which the Israelites obtained over the Canaanites, v. 3. A strong party was sent out, probably under the command of Joshua, which not only drove back these Canaanites, but followed them to their cities, which probably lay on the edge of the wilderness, and utterly destroyed them, and so returned to the camp. Vincimur in praelie, sed non in bello-We lose a battle, but we finally triumph. What is said of the tribe of God is true of all God's Israel, a troop may overcome them, but they shall overcome at the last. The place was called Hormah, as a memorial of the destruction, for the terror of the Canaanites, and probably for warning to posterity not to attempt the rebuilding of these cities, which were destroyed as devoted to God and sacrifices to divine justice. And it appears from the instance of Jericho that the law concerning such cities was that they should never be rebuilt. There seems to be an allusion to this name in the prophecy of the fall of the New Testament Babylon (Rev. 16:16), where its forces are said to be gathered together to a place called Armageddon-the destruction of a troop.