The evil in a person is regarded as evil only when one feels that it is evil. That is, the extent that the evil prevents him from receiving abundance determines the measure of the evil.
Normally, if one loses a penny to one’s friend, he does not hate him for this, since a penny is not important enough to fight with the other over it. But to the extent that his friend causes him losses, the level of hatred forms in him until he cannot stand him.
It follows that to the extent that a person has importance of Torah and Mitzvot [commandments], to that extent he can determine the measure of hatred for the evil, which interferes with his engagement in Torah and Mitzvot. For this reason, if a person wants to come to hate the evil, he must increase the importance of spirituality.
At that time, he will receive such a measure of hatred that will remove him from befriending his evil, as it is written, “You who love the Lord hate evil.” That is, to the extent that a person loves the Creator, so he hates those who interfere with loving the Creator.