G-d is in control of everything. Evil can only exist if G-d deems it so. Think about this mind blowing idea G-d created evil so we can defeat it.
The only way we can defeat evil is for us to line up our soul with G-d and thus G-d will work through us and evil will be defeated.
It is not us alone who can defeat evil. We can only do this with the help of G-d.
“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.
[Moses told the Jewish people,] “If you go out to war upon your enemies, G‑d will deliver [your enemy] into your hands, and you will take [back your enemy’s] captives.” Deuteronomy 21:10
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.1 Sefer HaSichot 5749, vol. 2, pp. 677 ff