We conquer and neutralize all the forces of evil by keeping the unity between us. They are no longer necessary because all the forces belong to one force: There is none else besides Him, the good that does good. But it is felt as good only if a person yearns for the good according to his level and his ability.
If he doesn’t yearn for that, the same force operates in an opposite manner. Its action is still good and benevolent to the sinners and to the righteous, of course, but a person who is inclined oppositely from the good and the benevolent feels this force as evil. This evil is revealed in different manners according to the attributes and desires that he has to correct by the same Light that Reforms. So it is in this Light that he feels darkness, like a bat that is blinded by the sunlight, in contrast to a rooster that gladly receives the dawn.
From the Preparation to the Daily Kabbalah Lesson 10/13/13