John Calvin Commentary Deuteronomy 20:15

"Thus shalt thou do unto all the cities which are very far off from thee, which are not of the cities of these nations." — Deuteronomy 20:15 (ASV)

Thus shalt thou do unto all the cities. An exception is introduced: the Jews were not to apply the common laws of war to the Canaanite nations, for whom the sentence of extermination had already been passed.⁴⁸

For God had not only armed the Jews to carry on war with them, but had appointed them to be the ministers and executioners of His vengeance.

We have elsewhere explained that there were just reasons why He determined that their race and memory should be utterly destroyed. This was especially so because He had patiently endured them for four hundred years, while in their wicked obstinacy they had not ceased to grow worse and worse, from which their desperate impiety was evident.

What had been said before is here, however, repeated; that is, since that land was consecrated to God’s service, its inhabitants were to be exterminated, who could do nothing but contaminate it. Therefore, this would be beneficial for the Israelites, lest by their deceptions they should be drawn into false superstitions.

⁴⁸ Addition in Fr., “et l’execution commise aux enfans d’Israel;” and its execution committed to the children of Israel.., “et l’execution commise aux enfans d’Israel;” and its execution committed to the children of Israel.