Calvin's Commentaries, Vol. 6: Harmony of the Law, Part IV, tr. by John King, [1847-50], at sacred-texts.com
A Repetition of the same History
40. And king Arad the Canaanite, which dwelt in the south in the land of Canaan, heard of the coming of the children of Israel.
40. Audivit autem Chananaeus rex Arad (is vero habitabat in meridie in terra Chanaan) quum ingrederentur filii Israel.
40. And king Arad the Canaanite. Although Moses gives no account of a battle, yet he briefly revives the recollection of the previous history; as much as to say, that in this part of their journey the Israelites at length met with their enemy, since they then began to fight with one of the nations of Canaan. In a word, the meaning is, that this was the beginning of their warfare, when the land which God had promised them as an inheritance was about to be occupied.