Deuteronomy Chapter 20    

“heart melt.” This is an idiom for a person losing courage.

“All its males.” The Hebrew uses the word for “male” here, not “man,” which can mean “person; human.”

“the mouth of the sword.” The idiom, “the mouth of the sword” is used to show great destruction, as if the sword was eating its victims (see commentary on Josh. 6:21).

“you are not to save alive anything that breathes.” The inhabitants of the Promised Land, Israel, were genetically corrupt in a way that made them evil and they could not be healed in any way, so God commanded that they be killed off (see commentary on Gen. 6:4).

“Devote them to destruction, yes, destruction.” God commanded that the nations inhabiting Canaan be completely destroyed, and He emphasized that fact by using the figure of speech polyptoton, where a verb is repeated twice but with different inflections, in this case, the verb “devote to destruction.” The Canaanite nations had been genetically corrupted by Nephilim, and could not be godly or redeemed. They had to be destroyed.

[For more on polyptoton, see commentary on Genesis 2:16.]

[For information on the Nephilim, see commentaries on Genesis 6:2 and 6:4.]

“so that they do not teach you.” Note that there is no consideration that the Israelites would teach the Canaanites about Yahweh. As a group, they were genetically evil, although there were some of them that were not genetically tainted, such as Rahab the prostitute and her family.

“you must not destroy its trees by swinging an axe against them because you can eat from them.” This is logical and kind. Also, after the conquest, the people who then inhabit the city will still be able to eat from those trees. Fruit trees take many years to be truly productive, so cutting down fruit trees takes away food from people for many years after the siege.