John Calvin Commentary Deuteronomy 2:9

"And Jehovah said unto me, Vex not Moab, neither contend with them in battle; for I will not give thee of his land for a possession; because I have given Ar unto the children of Lot for a possession." — Deuteronomy 2:9 (ASV)

And the Lord said unto me, Distress not the Moabites. He had previously forbidden them to enter the land of Edom unless consent were obtained. A similar prohibition is now added concerning the Moabites, because God had allotted to them the territory they inhabited.

As I have said, this was painful and burdensome: that they should cherish kindness and fraternal goodwill towards those who treated them with hostility. But God desired in this respect also to prove the obedience of His people.

He did not, then, take into consideration what this nation had deserved; but, since they were the descendants of Lot, and consequently of the lineage of Abraham, He desired to treat them with special favor.

For the division of the whole world belongs to Him, so as to distribute to its various peoples whatever part He chooses, and to fix the boundaries within which they should confine themselves.

If anyone objects that the people of Canaan also had their limits assigned to them and, therefore, should not have been expelled from the lands their ancestors had inhabited for many ages, the reply is easy. Namely, God is always free to take away what He has given and to readjust the boundaries imposed by His will when the sins of people deserve that this should be done.

Therefore, when He declares that He had given their land to the Moabites, it is not according to the ordinary meaning of the expression, but by a fixed decree that their dwelling place should remain sure and undisturbed.