Atheists often cite the existence of evil as a disproof of God. But the existence of evil actually disproves atheism. How can that be?
Because evil doesn’t exist on its own. It only exists as a lack or a deficiency in a good thing.
Evil is like rust in a car: if you take all of the rust out of a car, you have a better car; if you take the car out of the rust, you have nothing. Evil is like a cut in your finger: if you take the cut out of your finger, you have a better finger; if you take the finger out of your cut, you have nothing. In other words, evil only makes sense against the backdrop of good. That’s why we often describe evil as lacks in good things. We say someone is immoral, unjust, unfair, dishonest, etc.
So evil can’t exist unless good exists. But good can’t exist unless God exists. In other words, there can be no objective evil unless there is objective good, and there can be no objective good unless God exists, because His nature is, by definition, what we mean by objective “Good.” As Jesus declared, “No one is good—except God alone.”
We could put it this way: The shadows prove the sunshine. There can be sunshine without shadows, but there can’t be shadows without sunshine. In other words, there can be good without evil, but there can’t be evil without good; and there can’t be objective good without God. So evil may show there’s a devil out there, but it can’t disprove God. Evil actually boomerangs back to show that God exists.
This may sound counterintuitive, but if evil exists then God exists—not because God is doing evil, but because God is the standard of Good that is necessary to make evil even possible.
So when people assert that God can’t exist because of the existence of evil, ask them, “What do you mean by evil?” They will have a very hard time defining it with appealing to good. When they appeal to good, they are actually appealing to God’s nature. In fact, they are stealing from God to even make sense of their complaints. They have to sit in God’s lap to slap His face. (For more on this, and why God allows evil to continue, see chapter 5 of Stealing from God)