There is a certain strain in esoteric thought that considers evil to be necessary for good to come about, a kind of resistance required for good to arise by virtue of being forced to push back against it. According to this understanding, evil is simply the darkness against which one can more clearly see the light.
I completely reject that idea. Evil is evil, full stop.
At the same time, God is God and can make good come out of evil but that does not justify evil in any way. It remains wrong and a result of the fallen ego. Lucifer is not Christ's dark twin in some mysterious way working with him for long term evolutionary benefit. He is not there to enable self-consciousness to arise and grow. He is not a misunderstood good guy. He is a rebel against God not a partner with him. It's important not to get sucked into this false idea. Sin does not have to be experienced in order to overcome it. Darkness does not have to be integrated in order for a person to be in some sense whole. Evil is not part of good. Judas was not Christ's true disciple doing his work as a form of self-sacrifice. These are all deceptions and have no part in proper holiness. To believe that evil is anything other than evil will corrupt the soul. It is like peering into the abyss. Do that and you risk being drawn in.
I was prompted to write this post after reading a comment that Bruce Charlton made on his blog disagreeing with Rudolf Steiner who apparently believed that Lucifer was 'not really evil' but a kind of evolutionary force that could go wrong but was fundamentally positive. See the comment here at 17.57. Some of the Gnostics also thought this. I disagree with Steiner as well and so does someone else who knows better than any of us. "Woe to the world because of offenses! For offenses must come, but woe to that man by whom the offense comes!" (Matthew 18:7)