Moses told the Jewish people that after they conquer the Land of Israel from its occupiers, they would be allowed, if necessary, to attack neighboring countries that posed a threat to their security.
When we contend with evil, we are “going out to war.” We are “going out” of our true selves, for waging war is unnatural. Our soul’s native environment is the peaceful, infinite Divine consciousness it experienced before it entered the body.
Since our souls originate in G-d’s essence, and evil has no power against G-d’s essence, we have the upper hand over evil even before the battle has begun. We are “upon” — i.e., above our enemies. In addition, G-d only created evil in the first place in order for us to vanquish it. For both these reasons, the Torah goes on to assure us that “G-d will deliver your enemy into your hands.”
The Torah thus teaches us that in order to win the war against evil, we must identify with our Divine soul. We are then backed by the full power of G-d’s holiness.