These are important questions!
If God is all powerful, he could stop wars and famine and genocide. Why doesn’t he
I can’t imagine anyone could look at some of the atrocities that have happened in history and around the world today and question God’s goodness. For me, these events are clear evidence that we live in a sinful world that is not how it is meant to be. I think the problem here is free will. God has given humans free will to act as free agents in charge of our own lives and behaviour. So at what point should God override our free will, step in and stop the violence? If a drunk driver swerves towards a cyclist, should the hand of God step in and redirect the car? If a schoolchild pushes another child in the playground, should God step in and restrain the child? And if God always intervened to prevent every tragedy, what would that mean for our identity and experience as humans? It’s a big question.
if I pray to God for an answer and then an idea / thought comes to my head, how do I know if it’s God or not? What about people who commit terrible crimes and say “it is God’s will”?
You’re right that some people think they are hearing God’s voice and are actually experiencing serious mental health problems, or are otherwise deluded. I think there are lots of sensible things we can do to discern God’s will. Does the idea keep coming back, when we pray about it? Do those who know us well and love us think this would be a good idea for us? Does it accord with Christian teaching and is it an ethical thing to do? If we start to test it (apply for the job etc) does it seem to work out? Does it feel right?
how do you know if a good thing happened because of God and isn’t just a coincidence?
Interesting! Yes statistically coincidences happen sometimes. That’s a mathematical fact! But think for people who have a theistic world view, they see the hand of God in everything since God made the world. The Christian description for this is providence. So is it a coincidence that I bumped into my friend in town and we had a good chat? Yes, probably! Can I also be thankful for God that it happened and count it as a blessing? Yes, if I believe God’s providence is all around us all the time.