32. The True Nature of Evil
Sometimes the absence of a property is like a property itself. The absence of heat is cold. The absence of light is darkness. The absence of sight is blindness. The absence of life is death. Even though these negative conditions could be thought of as the "default," one who removes heat, light, sight or life could be said to be creating cold, darkness, blindness or death. [III, 10]
These conditions need not be created by actively removing something formerly present. God can create a person able to speak; if He does not give a person that ability, He has effectively created that person mute through His inaction. Similarly, if one person has the ability to save another person's life and he refrains from doing so, he has killed that person through his inactivity.
With this in mind, let us take a look at Isaiah 45:7. In this verse, God says, "I form the light and create darkness; I make peace and create evil."
Note the use of the same verb (borei - create) for both darkness and evil. In this verse, God is telling us that He actively forms things that exist, like light and peace. He passively creates the things that are only the absence of other things, like darkness and evil. (The Rambam deems "create" to be the appropriate verb as this is the word used during the original six days of creation. Since God created the universe ex nihilo - out of nothing - we see that the word is appropriate when discussing things that have no existence of their own.)
All negative things, like darkness and death, are merely the absence of positive things, like light and life. This is equally true of evil, which is an absence of good. God does not actively do "bad" things; everything He does is inherently good. Genesis 1:31 says that "God saw everything that He had made and, behold, it was very good." Bereishis Rabbah on Genesis chapter 1 tells us that no evil comes from above. Yes, there is evil in the world, but it does not actually "exist" as good does. Good is a real thing and evil is the lack of it.
The fact that evil is the absence of something is also true of the evils that humans inflict upon one another. [III, 11] People do bad things to one another for a variety of reasons, whether because of their passions or because of differences in ideology. Whatever the reason, it ultimately stems from ignorance, which is an absence of wisdom. Because of their ignorance, people do horrible things to themselves and to one another. If they possessed wisdom, they would work on improving themselves and society. This is the meaning of such verses as Isaiah 11:6, "The wolf will dwell with the lamb and the leopard will lie down with the kid...." In Messianic times, people will know the truth. Because of this knowledge, they will not devour one another like animals. Rather, they will coexist peacefully.
This point is made overtly a few verses later, in Isaiah 11:9, "They will not hurt or destroy in My holy mountain because the Earth will be full of the knowledge of God, as the waters cover the sea." Again we see that evil is not a presence, it is an absence - in this case, of the knowledge of God.