Many modern day and classical theologians are under the impression that God is a good God. In that God does not do evil and if God did anything other than good he would cease to be God. But God is the creator of all things, if anything is existence than it was created by God. Because God always has been there was nothing before Him, and since He created all nothing was created other than by Him. That leads one to believe that in some form God is responsible for the creation of evil. Not saying that God necessarily created the evil but created the means in which that evil could come about. C.S Lewis, in his book Mere Christianity, describes evil as nothing other than the perversion of good. So God created the good and it was perverted due to some other action other than His own. Since God is a good God He cannot operate with the realm of evil and doing so would change Him from being good. But since God, in a sense, created evil he would be capable of operating within it because it is His creation. But since operating within it would make Him cease to be good He has limited His abilities to operate within the concept of evil. That is not to say that He cannot redeem evil that is to say he does not partake in doing anything that is evil.
The fact that evil is a perversion of good comes from the understanding that humans have the free will to pervert that which is good. Even to the point that a human can know what is truly good and still is capable of doing the exact opposite. This is a gift from God due to the fact that God wants humans to choose to love Him and a forced love, or one without free will, is not a true love but an obligation. So because God created humans and has reign over them and has ultimate power of every facet of their life He has the capabilities to control everything about them. But because he operates under concept of Love He cannot force humans to do anything, and any attempt to do so would be a removal of free will. So God has again limited his capabilities out of love for the human race.
God is ultimate good and is capable of having ultimate control of everything in the entire cosmos of existence. But because God is Love and has love for his creations he has taken certain measures in which he limits his abilities. This does not speak to a lack of power to a most powerful God, but speaks to the complex and complete Love that is God. For one to relinquish power over another individual shows that that being has true love for the other.