As discussed previously in the first message in this series, the Kalam Cosmological Argument (which turned out to be the first entry in this series of apologetics fails), mercy is the suspension of justice.
An example of that might be a person who stands convicted in a court of negligent homicide due to drunken driving. The accused “throws himself on the mercy of the court,” citing he has reformed his ways, he has children to feed, &c. Instead of throwing the accused in jail for killing someone, the judge listens to his tale of reformation and places him on probation instead. The judge has shown mercy to the accused. It is not justice for the family of the victim.
According to Christianity (accepting Jesus on your deathbed) or Islam (accepting Allah on your deathbed), that act negates all the horrible things one did in the past. According to both, if you are sincere, your fate is Paradise, not Hell.
Which leads us to the problem of evil. If God is omnipotent, omniscient, and omnibenevolent, then God should know about all this. Calvinist versions of Christianity are even worse about it: Not only can you not be “saved” unless God wills it, but you cannot be “unsaved” even if you subsequently reject the claims of a god. In Mormonism, you can be baptised a Mormon after you have already died, thus gaining eternal reward—Bill Mahar did a famous “unbaptism” of former Massachusetts Governor Mitt Romney’s (R) father-in-law Edward Davies (an atheist):
(6:04, with much hilarity upon Mr. Maher’s “unbaptism” ceremony)
The Problem of Evil in Christianity starts with a quote from the Bible, Isaiah 45:7.
"I form the light, and create darkness: I make peace, and create evil: I the Lord do all these things." (KJV)
Quite clearly, God created evil. For an omnibenevolent god, that seems like a pretty crappy thing to do.
The ancient Greek philosopher Epicurus stated it as a syllogism:
Premise 1: If an omnipotent, omniscient, and omnibenevolent god exists, then evil does not.
Premise 2: There is evil in the world.
Therefore, an omnipotent, omniscient, and omnibenevolent god does not exist.
Nearly every Christian sect on the planet has tried to explain away this thousands-year old syllogism, but they cannot. The premises are true (with the definitions of the terms given), therefore the conclusion is true. As an aside, you won’t hear Isaiah 45:7 read in Sunday School or in a sermon: That verse is very inconvenient to the idea of omnibenevolence.
As I’ve noted before, the Problem of Evil presupposes that a person has free-will to follow the commands of God or no. Thus a murderer chooses to murder in violation of God’s commands. The problem here is the victim likely did not choose to be murdered (there was no free will available to the victim).
Tracie Harris of the Atheist Community of Austin puts the Problem of Evil in the form of a story (which I briefly noted previously where she manoeuvred a Christian to argue that child rape was the will of God). With the promise of eternal punishment, God says “I’m going to close the door, and you can rape that child. When you’re done, I’m going to punish you. If I did that, people would think I was a freakin’ monster. The difference between me and your god is if I saw a child rape, I would do what I could to stop it.”
What Ms. Harris didn’t get to (because the caller said the child was not an innocent victim—Christianity argues all people are flawed unless they accept Jesus and Matt Dillahunty hung up on him) is that in her example, if the rapist sincerely accepts Jesus on his deathbed, he goes to Heaven according to Christian theology.
That is the Problem of Evil in practice: It lets you off the hook for the most heinous crimes, by suspending justice for mercy. In secular morality, if the rapist is caught and tried, he goes to jail.