Sorry, the answer inevitably involves free will, beginning with Satan’s choice to deny God, and Adam’s choice to eat the forbidden fruit.
Do I take it that Sproul is a Calvinist who denies that God gives man the freedom to choose? If so, then, indeed, the explanation is difficult.
Two good places to start are Milton’s “Paradise Lost” and C. S. Lewis’s “The Problem of Pain.”
I think evil is strictly a human trait. I do not believe that evil even exists to God.
Many of my superstitious South American Christian/Catholics believe God would answer prayers for good care, when God is mostly about the resilience of good despite adversity, and that is a the realest of all gifts: ie. That of Job, Jesus etc...
there is not a prophet that did not suffer the robbing of God that occured in the Garden of Eden and doubled down with Jesus.
Want to find a good person from a bad one: simply check how they would treat God if He was omnipotent vs. how they would treat Him if He was not when He was in the flesh and just like us.
God can be omnipotent and still permit freedom of action. Otherwise, his creation would be nothing more than robotic...and that wouldn't be interesting to God or anyone else.
Life is life because it is free to choose and act.
That's the long and short of it.
Meanwhile the believer can take comfort in this.
Romans 8:18 For I consider that the sufferings of this present time are not worth comparing with the glory that is to be revealed to us.
God could have,
1. made us (and angels) with no moral standard or sense or deprived us from the moral ability to respond to or choose good [morally insensible].
2. granted us free moral agency, but never have given us anything to choose between [negation of moral choices].
3. called man to make the Creator their ultimate object of spiritual affection and allegiance and source of security is what is right and what is best for man, versus finite created beings or things, and provided moral revelation and influences. But always have moved us to do good, and never have allowed us to choose evil (such as make believing in God and choosing good so utterly compelling — like God appearing daily and doing miracles on demand, and preventing any seeming evidence to the contrary so that no man could attempt excuses [effective negation of any freedom to choose].
4. allowed us to do evil, but immediately reversed any effects [negation of moral consequences].
5. allowed us to do bad, but restricted us to a place where it would harm no one but ourselves [restriction of moral consequences].
6. allowed us to choose between good and evil, and to affect others by it, but not ultimately reward or punish us accordingly [negation of eternal consequences, positive or negative].
7. given us the ability to choose, and alternatives to chose from, and to face and overcome evil or be overcome by it, with the ability to effect others and things by our choices, and to exercise some reward or punishment in this life for morality, and ultimately reward or punishment all accordingly [pure justice].
8. restrained evil to some degree, while making the evil that man does to work out for the good of those who want good, and who thus love God, who is good.
9. in accordance with 8, the Creator could have chose to manifest Himself in the flesh, and by Him to provide man a means of escaping the ultimate retribution of Divine justice, and instead receive unmerited eternal favor, at God’s own expense and credit, appropriated by a repentant obedient faith, in addition to the loss or gaining of certain rewards based on one’s quality of work as a child of God. And eternally punish, to varying degrees, those whose response to God’s revelation manifested they want evil, [justice maintained while mercy and grace given].
http://www.conservapedia.com/Theodicy