Yoav instructs his soldiers in much the same way as today’s soldiers of Israel are instructed. The soldiers must strengthen themselves to go into battle, fighting to protect the People of Israel and the cities of God. Hashem will respond by doing what is right in His eyes. Ralbag notes that in most cases, God expects of humans to do their part and not to rely on a miracle. Once people do what is expected, Hashem may choose to provide miracles and redemption. Nowadays, this is a daily occurrence for the soldiers of the Israeli Defense Forces, who strengthen themselves for battle and have often been rewarded by God with miracles.
Source: Israel in the News