Numbers 21:1

The Canaanite heard. He heard that Aharon died, and the clouds of glory departed, etc. as stated in Rosh Hashanah. Amelek was always a whip for disciplining Israel, prepared, at all times, to mete out punishment.

Who lived in the south. This was Amalek, as it is said, “Amelek dwells in the southern part of the land.” They changed their language, and spoke in the Canaanite tongue, so that the Israelites would pray to the Holy One, Blessed is He, to deliver the Canaanites into their hands —but they were not Canaanites. The Israelites saw that they were dressed in Amalekite clothing, but spoke the Canaanite tongue. They said, “let us pray in a general way,” as it is said, “if you will deliver this people into my hand.”

By the route of the spies. The negev route traveled by the spies, as it is said, “they went up to the negev.” Another interpretation of דֶּרֶךְ הָאֲתָרִים ; the route of the great pathfinder which traveled before them, as it is said, “[the Ark of the covenant of God traveled before them] three days’ journey, to seek out a resting place for them.”

He took from them a captive. It was only one maidservant.

And Amalek, who had dwelt in the south, and changed, and came and reigned in Arad, heard that the soul of Aharon was at rest, that the pillar of the Cloud which for his sake had led the people of the house of Israel had been taken up, and that Israel was coming by the way of the explorers to the place where they had rebelled against the Lord of the world. For, when the explorers had returned, the children of Israel abode in Rekem, but afterward returned from Rekem to Motseroth, in six encampments during forty years, when they journeyed from Motseroth, and returned to Rekem by the way of the explorers, and came unto Mount Umanom, where Aharon died; (and,) behold, he came and arrayed battle against Israel, and captured some of them with a great captivity.

AND THE CANAANITE, THE KING OF ARAD, HEARD. We find [mentioned] amongst the conquests of Joshua: the king of Arad, one. of the river Jordan: so how — as indicated in this section — could its king fight against Israel whilst they were still on the eastern bank of the Jordan: Moreover, in the section dealing with the [stages of the Israelites’] journeyings [in the wilderness], it is written, And the Canaanite, the king of Arad, who dwelt in the south in the land of Canaan, and Scripture does not refer to [that land which is] on the eastern side of the Jordan as “the land of Canaan” without qualification, just as He said, the land of Canaan according to the borders thereof., 34:2. Verses 10-12 ibid., define the eastern boundary of Canaan as the Jordan: hence we see that the word “Canaan” does not include land east of the Jordan. So the question reappears: how come that the king of Arad, a land west of the Jordan, came to fight the children of Israel who were now encamped east of the Jordan? Furthermore, [if Arad was to the east of the river Jordan], Moses should have given the land of the king of Arad to one of the tribes of Israel [as their inheritance, in the same way that he divided up the other lands which he conquered]; but Scripture always tells, Verses 13-15; Joshua 12:6, etc. that it was the land of Sihon and Og, the two Amorite kings, which Moses gave to the two tribes [Reuben and Gad] and to the half-tribe [of Menasheh], whereas the nine tribes and the [other] half-tribe [of Menasheh] received their inheritance after they crossed the Jordan into the land of Canaan. Perhaps we may explain [that the reason for this is] that Israel utterly destroyed their land, and did not settle therein at all. But that is not [the] correct [explanation of the word v’hacharamti in Verse 2]. Similarly Rashi explains [that the expression: And Israel vowed a vow unto the Eternal, and said, If Thou wilt indeed deliver this people into my hand,] then ‘v’hacharamti’ their cities means that Israel would dedicate the spoils [of those cities] to the Most High [and not that they would destroy the cities themselves].
The correct interpretation appears to me to be that this king of Arad dwelt in the south on the western side of the Jordan, in the land of Canaan near the Jordan, bordering onto the land of the children of Judah, near Hebron which is in the south;. and he …