Charles Ellicott Commentary Numbers 21

And when king Arad ... — The verse may be rendered as follows: Now the Canaanite, the King of Arad, who dwelt in the south country (or, Negeb) heard (or, had heard) that Israel had come by the way of Atharim (or, of the spies), and he fought... The date of this occurrence is uncertain. The district of Arad appears to have extended to the southern frontier of Canaan (Joshua 12:14; Judges 1:16–17).

The attack probably took place either in the interval between the departure of the messengers to Edom and their return, or when the Israelites broke up from Kadesh, and before the direction of their march had been ascertained. The word Atharim, which is rendered in the Authorized Version spies, may be another form of the word which occurs in Numbers 14:6, and which is there rendered them that searched; or, as appears more probable, it may be the name of a place which does not occur elsewhere.

And they utterly destroyed them and their cities. —The meaning of the verb used here is to devote to destruction, and therefore to destroy utterly. It is not clear whether this destruction was carried out at once, or whether the fulfillment of the vow took place at a later period. (Judges 1:17.) If the attack of the Canaanites was made at the time of the final departure from Kadesh, the latter view must be maintained, as it can hardly be supposed that the cities could have been rebuilt and again destroyed in such a short interval.

And he called the name of the place Hormah. —Better, And the name of the place was called Hormah. The word Hormah — that is, a devoted thing —is cognate with the verb that occurs in this and the preceding verse, and which is rendered utterly destroy. The place is so called by anticipation in Numbers 14:45, and, as with other names (for example, Bethel and Jacob), the name was probably given anew to the place on a later occasion (Judges 1:17).

Because of the way— Better, in (or, on) the way. In addition to all the hardships and dangers of the journey, they were conscious that they were turning their backs upon the land of Canaan, instead of marching by a direct course into it.

This light bread.— The word rendered light denotes something vile or worthless. It was thus that the Israelites regarded the manna which was given to them from heaven; even as the “spiritual meat” which is given to Christ’s Church in His word and ordinances is too commonly regarded among us.

And the Lord sent fiery serpents ... — Hebrew, the serpents, the seraphim (i.e., the burning ones). (Isaiah 14:29; Isaiah 30:6.) The word appears to denote a particular kind of serpent, as in the following verse. Some think that they were so called because of the bright fiery red upon their heads; others because of the blazing sunbeams on their scales; and others because of their inflammatory and poisonous bite. Venomous snakes are said to still abound in the Arabah.