There are quite a few, more than I could put on this forum. The combination of all three books would probably near 500+ pgs. To give you an idea, they deal with the problem of pain (i.e. why doesn't God stop bad things from happening), the existence or non-existence of morals in a philosophy (that's a confusing statement which means, why are morals important to a philosophy), why God doesn't suspend the laws of science (i.e. why isn't he more obvious?), & the reason why the Judeo-Christian God is the only one capable of meeting the requirements of existence. I'm sorry if I've had to be hard to understand, I don't know how I could fit all that info in a nutshell any other way. Read the books, they'll explain it better than I can. 'Mere Christianity' is a good book to start on, it's easier reading. And it's only $8 from Amazon. I can try to explain it if you want, but I think it might be better to read it (it's easy reading).
Evan