John Calvin Commentary Genesis 36:9

"And these are the generations of Esau the father of the Edomites in mount Seir:" — Genesis 36:9 (ASV)

And these are the generations of Esau, the father of the Edomites. Although Esau had two names, in this place the second name refers to his descendants, who are called Idumeans. For, to show what God had bestowed upon him for the sake of his father Isaac, Moses expressly calls him the father of a celebrated and famous people.

And certainly, it greatly served this purpose to trace the effect and fulfillment of the prophecy in the descendants of Esau. For if the promise of God flourished so mightily toward a stranger, how much more powerfully would it manifest itself toward the children to whom belongs the adoption, and consequently the inheritance of grace?

Esau was an obscure man and a sojourner in that country. How then could rulers suddenly spring from him, and a great body of people flourish, unless it was because the blessing that proceeded from the mouth of Isaac was confirmed by the result?

For Esau did not reign in this desert without opposition, since a people of no insignificant name previously inhabited Mount Seir. For this reason, Moses relates that the men who had previously inhabited that land were mighty, so that it would not have been easy for a stranger to acquire such power as Esau possessed if he had not been divinely assisted.