Here are some tough questions for the Christian, depending on his or her particular theology:
Can God be surprised? Surprise is the basis of laughter. Can God laugh?
Can God think? Thinking means weighing alternatives. But if God knows everything then can God think?
Is God metaphysically free? Did God ever choose his character and his moral standards? Does God ever know what it is to make a choice?
Is God Good?
If God didn’t need anything, then why did he create us? To say God’s nature is love and he wanted to share his love with us doesn’t help for two reasons, 1) Most of us will end up in hell, which means he knowingly created heaven for the minority on the screams of billions of people who end up in hell; 2) If life was already perfect for God, then God did not need to share any more love with anyone else. Why break this purported perfect harmony for the pain of dealing with us and the pain of those who end up in hell?
Once God decided to create us, if he planned everything in advance as the Calvinist believes, or if he foreknew everything would happen with certainty, then why bother creating us? What’s the point?
What is the basis of God’s foreknowledge?
If God gave us free will and he knew we would abuse it so badly, then why give it to us? Isn’t it incumbent for the giver of a gift to be responsible for whom he gives that gift? And isn’t the giver of a gift blameworthy if he gives gifts to those whom he knows will abuse those gifts? Should we make drugs available to 8 year olds and alcohol available to 6 year olds? Would you give a razor blade to a two year old?
Can God create free creatures who always obey? For the Calvinist this would’ve been no problem, so why does it bring God more glory to decree what we see here on earth and later in hell, than one where we always obey? For the non-Calvinist Christian, what is different for those in heaven such that they will have free will and never disobey? Will there be sin and another rebellion in heaven? Why not? And if God can make people obey in heaven then why didn’t he first create us such that we always obeyed here on earth too?
Did God foreknow that Adam and Eve would sin? If so, then he would also know in advance the reasons why they chose to sin. And if he knew in advance what those reasons were, then he could’ve corrected them and/or provided them more evidence to believe him. If, for instance, Adam and Eve needed more evidence that God meant what he said if they eat of the fruit, then couldn’t God have given them more evidence, like he purportedly did to Moses and Gideon who both doubted? To withhold this needed evidence is to be at fault for doing nothing to help Adam and Eve in their temptation.
Why didn’t God create us with a propensity to dislike sin? We have an aversion to drinking motor oil. But we could still drink it if we wanted to. Why couldn’t God have created in us an aversion to sin like we have an aversion to drinking motor oil?
Why did God create the universe with a big bang and the slow long evolutionary development of galaxy, star and planet formation, and then all of a sudden “switch gears” and instantaneously create Adam & Eve in an instant? Was it harder to create the universe than the peak of his creation such that it took him billions of years to create the stuff of the universe but a snap of his fingers to create the apex and crowning jewels of his universe?
Why is a supposedly omniscient and completely understanding God so barbaric, even allowing slavery, knowing full well the suffering people would experience because it wasn't one of his ten commandments: "Thou shalt not own slaves nor buy and sell them for profit."
Why is a supposedly omnipotent God not able to stop the 2005 Indonesian tsunami that killed a quarter million people before it happened? If he had stopped that underwater earthquake from happening none of us would have known that he did and hence he wouldn’t have revealed himself in any ways he might not have wanted to. Since all it would have taken is a “snap” of his fingers to avert that tragedy then isn’t he morally responsible for it? If we were God we would be morally obligated to do so. Why isn’t God? And if he is morally responsible for it, then he wanted it to happen for some greater good. That’s right, he wanted it to happen. What is the greater good here?
Here's another good one by Dagoods. How is it that one member of the trinitarian Godhead can intercede on our behalf with another member of the Godhead? Does one member of the trinity, Jesus, know or want something that God the father doesn't? see here.