I read one time that the Devil's most powerful tactic is to make you believe that he doesn't exist. This logic makes sense, because if you don't believe that there are evil spirits roaming around, nothing can hurt you, you're not afraid. Even though that may not be necessarily a bad thing, I don't think God wants us to be afraid. Au contraire, I think he wants us to be brave, and to have complete free will. And in order to achieve that, we must be aware of the choices given to us, both the good and the bad. It's easy to have a free-for-all life, where there are no consequences for your actions. However, the weird logic lies when a person believes in a God, but no in the Devil. This is kind of like an attempt to believe on the good, but not on the bad. There are good and bad spirits roaming around, and we have to be aware of both of them, so we are not fooled.
I have never experienced pure evil, I'm not sure I know what that is. When I first read this, I thought about making a joke and stating that pure evil was my sister. But I've grown past the times I compared her to a demon. The essence of evil, I can't even begin to imagine. I think of something ugly and dark who does bad things to others to feed off their suffering. No, I have never experienced that, I've never witnessed it. The evil that has come into my life often has a shining aura, it's beautiful and tempting and there's precisely where its danger lies.