Who is cursed?
Radak: One who is in the war and slackens from killing. This was said only about [fighting] Mo'av, for Hashem had great anger against them, since Hashem commanded Yisrael not to afflict Mo'av, and they did evil to Yisrael.
What is "Meleches Hashem"?
Rashi: It is destruction of Mo'av, which is a Shelichus of Hashem.
Malbim: It is to remove Mo'av from the land, for via this they will have a bud [and sprout]. Therefore, one who does not leave and flee, and wants to stay in the place, he is fraudulent in Hashem's work. He is worthy to die through this, for he is cursed.
Is there another curse for one who does not kill?
Radak: The curse is doubled to strengthen the matter.
Malbim: This is a curse for one who does not kill those who remain, who are cursed.
