Based on what I know, evil is a consequence of rebelling against God, or trying to be equal or superior to God. In heaven, Satan, the rebellious angel, formed a worship circle and attacked and hurt the other angels. Subsequently, God created the universe as Satan's prison. Since Satan was imprisoned, he has not been back to heaven. Satan has, however, made attempts to escape the universe to return to heaven. This is were it gets really weird, like science fiction. Science has found dark ugly scars on the boundary of the universe. They are from attacks by Satan to escape the universe and return to heaven. There is only one rebellious angel, those legions of rebellious angels don't exist. Satan was the thirteenth angel. What remains in heaven is God and twelve angels. It is interesting, thirteen is an unlucky number and twelve is found throughout the Bible and in our everyday world. As for the issue of freewill, after God created an angel, He tossed it out into heaven. The angel had a choice of roaming around heaven or coming back to become part of the God's worship circle.
In short, evil is a consequence of rejecting God, or attempting to be a "god." The big problem with trying to become a god is it is a dark empty road full of nothingness. A creature has no power to create anything! Creatures can do things like invent or alter their environments. Satan's means of existence seems to be to subvert, deceive, hurt, and destroy God's creatures. It is a constant battle, God emits holiness, Satan attacks and destroys. Satanists strive to become rebellious creatures. The problem for Satanists is they are mortal creatures with limited life spans. Satan, a dark evil force, was created to be immortal. Subsequently, Satan will remain in it's prison until the end of time. Then, things will return back to the period when God was not threatened by a rebellious angel. Perhaps, it is more than you wanted to hear, just thought I'd put it out there.
