There are many good books by ex-Christians and other skeptics which do a great job of exposing the extreme improbability (and outright silliness) of the supernatural claims of Christianity. But if I had to pick just one book, I would pick: …the Bible!
Many Christians have read the New Testament but how many Christians have read the four Gospels in parallel? I encourage Christians to do that. Start with the first chapter of the Gospel of Mark (which most scholars believe was the first gospel written) and then read the same story (not necessarily the corresponding chapter number) in Matthew, then Luke, and then John. Do this for every chapter and story in Mark.
And if you are really ambitious, once you reach the chapter in Mark where Jesus leads his disciples out to the Garden of Gethsemane on the night of his arrest, read Roman Catholic New Testament scholar Raymond Brown’s masterpiece The Death of the Messiah as he reviews each pericope in the Gospel of Mark in parallel with the same story in the other four Gospels.
I believe that if you are a conservative Christian, just reading the Gospels in parallel in your own Bible and reading Brown’s commentary on them (Brown very much believed in the supernatural, miracles, the empty tomb, and in the bodily resurrection of Jesus), you will be shocked and amazed at what you learn about your Bible and Christianity.
End of post.