If God is taken to be a sentient omnipotent omniscient omnibenevolent deity there is no satisfactory explanation for the existence of evil. All rational analysis, given God's assumed properties, lead to contradiction.   

The problem of evil is not the existence of evil, but faulty assumptions about the nature of God that lead to inexplicability of the existence of evil.

If the nature of God is understood then the existence of evil is natural and necessary. The fact and necessity of a finite speed of light is related to the fact and necessity of evil. The forward progress of the evolution of physical reality and its life and consciousness must be opposed, otherwise an existential (and mathematical) singularity would result.

REP holds that balance is the ultimate constraint determining the architecture of reality, and good without evil would be imbalance. A minor thread of imbalance is required within an overarching balance in order to confer evolution with directionality.