LOL
I'll repeat it, but there's no answer!
If God is all-good and omnipotent...
Why does evil exist?
IOW, is there some evil in God?
Is He not able to remove evil from the universe?
It IS a problem within Christianity and the one question for which there is no answer.
Good ole' Augustine thought he had the answer in his new Christian days. But, as usual with him, he did change his mind later on in life and deided that, indeed, there was no answer to this problem.
THE PROBLEM OF EVIL
One question preoccupied Augustine from the time he was a student in Carthage: why does evil exist in the world? He returned to this question again and again in his philosophy, a line of inquiry motivated by personal experience. Augustine lived in an era when the pillar of strength and stability, the Roman Empire, was being shattered, and his own life, too, was filled with turmoil and loss. First he lost his mistress, then his mother, and finally his son. To believe in God, he had to find an answer to why, if God is all-powerful and also purely good, he still allows suffering to exist.
Augustine’s answers to this question would forever change Western thought. First, he states that evil exists because we have free will. God enables humans to freely choose their actions and deeds, and evil inevitably results from these choices. Even natural evils, such as disease, are indirectly related to human action, since they become evil only when in contact with people. According to this theory, a disease spreads only because men and women put themselves in harm’s way. Augustine gave a more theological explanation later in his life: we cannot understand the mind of God, and what appears evil to us may not be evil at all. In other words, we cannot judge God’s judgment. The roots of both of these answers stemmed from two philosophies, Manicheanism and Neoplatonism, which shaped Augustine’s ideas.
source: SparkNotes: Saint Augustine (A.D. 354–430): Themes, Arguments, and Ideas
Is God the author of evil or its helpless victim? St. Augustine's answer has been the most intellectually credible and emotionally satisfying solution to this vexing problem.
One doesn't need a Ph.D. in theology to look around the world and realize something is desperately wrong. The existence of evil is one of the most vexing challenges a Christian--or any person, for that matter-- must grapple with. It's occupied the minds of great Christian thinkers since the beginning, including St. Augustine (354-430). For much of his life he worked hard at a solution.
source: Augustine on Evil | Stand to Reason
This is more complete and also mentions John Calvin at the end of the article and how he accepts that God created evil.
Augustinian theodicy - Wikipedia
And this speaks of how he changed his mìnd on the millenium, but it's not the only concept.
Why Saint Augustine Changed His Mind About the Millennium
Is sin the problem or is unforgiven sin the problem?
Is sin part of the solution to man’s problem (man fulfilling his earthly objective)?
Would you prefer to be in a place where your eternal close relationship with God was dependent on your personal ability to obey God forever or in a place where your eternal close relationship with God is dependent on your just accepting God’s charity?
Let me explain:
The reason you have free will is because it is required for you to complete your earthly objective.
This messed up world is not here for your pleasure, but to help you become like God Himself in that you have the unique, unbelievable Godly type Love (God himself is Love).
God has created beings to shower them with the greatest gifts possible, the greatest gift being having a Love like His.
If there is this Creator of the universe out there, His “creations” could not really “do” anything for Him, so this Creator would have to be seen as a Giver (Unselfish Lover) and not trying to “get” something from His creation.
Why would God have a totally unselfish type of Love, since He personally would not get anything out of it? If God’s “Love” is some kind of knee jerk reaction, then it is really meaningless (something like; gravity which is nice to have, but everyone automatically has it). God Loves us in spite of what we have done, who we are or what we will do, so it has to be by His choice.
So God would create the right universe for the sake of the individuals that will accept His gift (the most powerful force in all universes, since that force compels even God to do all He does) and thus we become like He is (the greatest gift He could give).
What keeps the all-powerful Creator from just giving whatever He wants to his creation, eliminating the need for free will and this earthly time:
There are just something even an all-powerful Creator cannot do (there are things impossible to do), the big inability for us is create humans with instinctive Godly type Love, since Godly type Love is not instinctive. Godly type love has to be the result of a free will decision by the being, to make it the person’s Love apart from God. In other words: If the Love was in a human from the human’s creation it would be a robotic type love and not a Godly type Love. Also if God “forces” this Love on a person (Kind a like a shotgun wedding) it would not be “loving” on God’s part and the love forced on the person would not be Godly type love. This Love has to be the result of a free will moral choice with real alternatives (for humans those alternatives include the perceived pleasures of sin for a season.)
This Love is way beyond anything humans could develop, obtain, learn, earn, pay back or even deserve, so it must be the result of a gift that is accepted or rejected (a free will choice).
An unselfish God would be doing all He can to help willing individuals to make that free will decision to accept His Love. Again, since God will not be forcing these individuals, they have to be willing (it is their choice) and God cannot “make” them willing since that is robotic action. God can only at best make them free will agent (like God is) and capable of make the right decision without the selection being worthy of anything (it is a gift of pure charity).
This “Love” is much more than just an emotional feeling; it is God Himself (God is Love). If you see this Love you see God.
Let me just give you an example of How God works to help willing individuals.
All mature adults do stuff that hurts others (this is called sin) these transgressions weigh on them burden them to the point the individual seeks relief (at least early on before they allow their hearts to be hardened). Lots of “alternatives” can be tried for relief, but the only true relief comes from God with forgiveness (this forgiveness is pure charity [grace/mercy/Love]). The correct humble acceptance of this Forgiveness (Charity) automatically will result in Love (we are taught by Jesus and our own experience “…he that is forgiven much will Love much…”). Sin is thus made hugely significant, so there will be an unbelievable huge debt to be forgiven of and thus result in an unbelievable huge “Love” (Godly type Love).
If the nonbeliever had knowledge of God's existence that person would not need faith in God's existence, but faith is needed for humility and humility is needed to humbly accept pure charity and the only way to get Godly type Love is through accepting it as pure charity in the form of forgiveness.
That is an introduction to a huge topic.