An excerpt from "What Christians Believe & Why We Believe It!"
© Patrick C. Marks, 2022
All rights reserved.
Short answer: Evil exists because of human freewill. God is all-good and all-powerful so at some point in the future, He will get rid of evil forever!
It is a reasonable thing to ask why the Christian God allows evil in the world - because if God exists and is really all-good, He would certainly want to do something to get rid of evil. If God is all-powerful, then He certainly can get rid of evil. But we look around the world and see every sort of evil, including evil things done in the name of religion. How can this be the case if God is so good and powerful? Some people think this situation means that God must not be all-good after all since He has not done anything about curing evil in the world. Others think this must means God is not all-powerful because He does not have the power to get rid of evil. Still others think the existence of evil means God does not exist at all.
The short answer from the Bible is that God has not rid the world of evil just yet. He has a purpose for allowing it to continue for a time, but in the end, He will rid the universe of evil forever. He has the power to deal with it and He will at the right time. The real question is why does God allow evil to exist even for a short time?
To answer this question, we first need to understand what evil is in the first place. There is a popular view of evil today that anyone can see in popular media such as the Star Wars movies. This is the idea that good and evil are equal forces struggling to stay in balance. If this is true, it means that good and evil are equal parts of the whole of this universe. If this is the case, then the ideal situation is for good and evil to balance each other out. It also means that evil is just the opposite of good, so in that kind of universe it follows that if there is a God, then the devil or Satan must be the opposite of God.
Even some Christians take this view. They think that since God created everything, and evil is a thing, then God must have created evil also. The problem with is view is it makes evil equal with good, but the Bible teaches God is all-good and is not the author of evil at all. Both ideas cannot be correct because if God created evil, and evil is not good, then God cannot be only-good.
The idea that good and evil are equal things is, however, false. This is so because a real thing is something that has an essence of itself. This means that a thing is something that exists as it should exist. Evil, however, only exists inside something else. Evil cannot exist as it should exist, because how something should be is a good thing, and evil is not good. This means that evil is only a lack of how something should be. Evil is, therefore, not a real thing at all. Evil is only a lack of something.
For example, think about blindness. Why is blindness in human beings evil? Blindness in human beings is evil because human beings have eyes that should see and how a human being should be is the essence of a human being. To understand this better, compare a human being with a rock. A rock is also blind, but blindness in a rock is not evil. Why? Because of the essence of a rock (what it is)! A rock is not a thing which should have eyes and be able to see, so blindness in a rock is not evil.
Where did evil come from?
The Bible teaches us in Genesis 1:27 and other places, that God created human beings in His image. We reflect the nature of God because God has freewill, and we have been given the power of freewill also. Freewill is the ability to do what we wish to do. We are not programmed computers and we are not just creatures of instinct either. We do have a sort of programming in our DNA that helps us with basic survival, but there is a part of us that can think about that programming. We can decide to do something that violates that programming. This means while we do have instincts, we have the power to choose beyond our instincts! For example, we have an instinct to save our own lives, but we can risk our lives or even sacrifice our lives for something we believe is more valuable. Values that we might think are more important than our genetic programming or instincts are called moral values. Our ability to make moral choices is our freewill, but if we choose to do something other than what is good, we make evil possible.
Freewill is the greatest good because God has freewill, and God is only good,  but if we do not have the ability to choose to do something other than good, then our decisions would not be free.  God created a universe where freewill is possible because only freewill can make personal love possible. In our culture today, many people link the idea of love with feelings - feelings that just sort of happen to a person (we supposedly fall in love as if it could not be helped). There is, however, a difference between feelings of affection or attraction that may come and go and true, personal love. A person who loves another person may have feelings of affection for the person he or she loves, but the act of love itself is a choice. Love is the decision one person makes to ignore self-interest so that he or she can bring about some good in the person being loved.  It is a sacrifice or an effort and only freewill makes it possible. If a person is merely programmed to say “I love you” or built to do only good things, the words “I love you” or the actions of doing good for someone else, would be nothing more than a computer program. There would be no choice involved if such actions were built-in or programmed and without choice such actions could not be personal or really meant.
So, love is a choice to set aside personal self-interests to freely bring about the highest and best good of another person because you sincerely want to do good for someone else. The Bible says that God is love in a pure sense. This is the reason God sacrificed His personal self-interests when He created the universe.  God could have built a universe with only the kind of creatures in it that are programmed to sing His praises and do things that interest Him, but any good done toward God in that kind of universe could not be personal. A pre-programmed creature cannot sincerely or freely give anything it is not free to do anything else. It only does what it is does - because that is what it does. In other words, without freewill, real love is impossible.
So, what happens when free human beings freely choose not to love God? Since human beings are created so that their highest and best form of existence is to be in real relationship with God, to refuse that relationship is to lack what we should be doing. Evil is a lack of what something should be, so the human being who chooses not to be in relationship with God is choosing the highest form of evil. He or she is choosing to love himself or herself rather than God. This is where evil (the Bible calls it sin) comes from because evil is elevating self-interest over the interest of other beings – especially elevating self-interest over God.
God allows human beings to do this, if they freely choose to do so, but only for a short time. As described above, God allows this so that real love can exist between Himself and human beings. There are, however, temporary consequences because of human freedom. Without relationship with God, human beings become more and more self-centered. Selfishness leads to taking advantage of other people because the selfish person wants whatever he or she wants and does not care about exploiting someone else to get it. This hardness of self-interest has led to every form of murder, theft, exploitation of others and every other form of human misery. The bad things that happen to human beings can be traced back to human freewill.
There are, of course, examples of natural disasters, genetic diseases, and the death of children that do not seem to be related to freewill. These horrific things are, however, also the result of human beings rejecting God. The Bible teaches that God originally created the world as a perfect place for human beings who were made to reflect His image. In that creation, there was no death, no disease, and no pain. There were no natural disasters or even accidents. Human beings were originally designed to live forever, just as angels do. When Adam and Eve chose to rebel against God, they brought a terrible curse on the earth. The Bible says that the wages, that is – the results, of sin is death.  After the first human beings used their freewill to reject God, creation itself was cursed and twisted. Animals that once ate only vegetables became carnivores. Microbes that once served a good purpose became disease. All living things were put under the bondage of death so that everything now decays and breaks down because of the curse of sin.
Why hasn’t God dealt with evil yet?
God has not destroyed evil yet because He is allowing a time for human freewill to exist. In the end, God will end the curse of death and bring back the perfection and the fulness of the creation. This is the great hope of the Christian faith. After a time to allow for freewill, God will confirm the freewill choice of every human being forever. Those who freely choose to be in relationship with God will enjoy that relationship forever. Those who refuse will exist alone with themselves forever. This is so because God will literally give people what they choose. Everyone can choose God or themselves, but either choice will be locked in forever.
God will not force people to choose a relationship with Him.  He will not do this because if He did, He would violate freewill. Freedom is not freedom if it is not free! He will, however, only allow human freewill for a limited time because God is all-good and all powerful. Since He is all-good, it is part of His nature to bring about perfection and good. This means He will defeat evil at some time in the future. In the meantime, God allows evil to bring about a good end – the existence of real love!
As finite creatures with a very limited understanding of all there is to know. We cannot see all ends. It is not always clear to us in the moment how some evil can ever accomplish a good purpose. We are, however, very limited in what we know. God knows everything so He can see how an eternal good can come about when a free human creature is allowed to experience a temporary evil. For example, in Genesis chapters 37 - 50, Joseph experienced the temporary evil of being made a slave in Egypt. He could not see in the moment that he was enslaved how that could bring about any good, but he trusted God. Now, Joseph had been given the gift of understanding dreams and the Egyptian culture was very superstitious. When Joseph was able to make sense of the king’s (Pharaoh’s) dream, Pharaoh interpreted this to mean Joseph had supernatural favor. So, Pharaoh elevated him to the second highest position of power in the country. Joseph went on to save the lives of nearly everyone in Egypt as well as the lives of his family during a famine. Joseph himself said, “…God intended it all for good. He brought me to this position so I could save the lives of many people.” 
There are some evils God allows in our lives today that can act as warnings also. Physical pain, for example, can warn us that something is wrong in our body. Physical pain can prevent us from doing further damage to ourselves. Mental or psychological challenges can cause us to reconsider how we are living or give us an intense reason why we should think about what we are doing. Enduring evil may also allow us to emotionally connect with others as a comfort to them because we have been through something similar.
Some people think that freewill does not seem like a good enough explanation to explain evil in the world. They think that if God knew freewill would lead to evil, why would He make a world at all? But nothing is not better than something because nothing is nothing and nothing has no value. This means that no-world at all is not better than this world, because no - "thing" (nothing) is 100% less than any - "thing" (anything). Besides, if God had created a universe where everything was robotic and programmed, then there would be no love and no morality. Without love and morality, the world could not be better than this one, because there would be no evil to be better than in the first place!
God has freewill and God is the highest of all goods. This means that freewill and love are the highest good. Since freewill and love cannot exist without true freedom of choice, it follows that this world where freewill and love are possible is the best way to get to an eternal world where freewill and love will rule forever.
 It is important to recognize that neither force in itself is good or evil. “Good” is the proper balance between the two; “evil” is an imbalance in either direction. (Winfried Corduan, Neighboring Faiths, 392-393)  In short, evil does not exist in itself. Evil exists only inside a thing or substance – In short, there has to be some good thing in order for evil to exist in it as a lack, corruption, or privation of it. God created all things, evil is not a thing, hence God did not create evil. (Geisler, Why Evil, 19)  God has free will. The Bible also reveals that man was created in the image of God (Gen. 1:27) and therefore also exercises free moral choice and assumes accountability. (Paul Ackerman, In God’s Image, 45)  Free will makes evil possible since it is the power to do otherwise and to do otherwise than good is evil. (Geisler, Why Evil, 29)  Love is “willing the good of its object” (Geisler, Systematic, 585)  Creation is an act of humility, of self-denial. It is a sacrifice, a gift. (William Dembski. Being as Communion, 15)  Romans 6:23  God cannot destroy evil without destroying free-will. “[God] cannot force anyone to freely accept Him. Forced freedom is a contradiction in terms.” (Geisler, Why Evil, 38)  Genesis 50:20b NLT  This is not the best world possible, but it is the best way to the best world achievable. A world of pain, danger, and sin is a necessary condition for attaining a world without any of these preconditions. (Geisler, Why Evil, 89-90)