Christians ask themselves questions that conveniently have answers in Christianity. Here are some questions that I'd like to see Christians ask themselves.
How many other religions have you studied?
Of all the world's possible religions, why do you think the stories of the Bible are more valid than the stories of the other religions?
If you were a Martian and landed on Earth having never heard of a concept of God, how would you decide which, if any, of the world's religions had merit?
If someday there would be definitive proof of the non-existence of God, would you still be a Christian?
Why do you believe what you believe? (Favorite question on The Atheist Experience)
If you knew with 100% certainty that you would be going to Hell, would you still be a Christian?
Of all the denominations there are, why do you belong to the one you belong to?
Have you read any of the scholarly theological literature of your denomination?
Have you read every word of The Bible?
How do you reconcile the inconsistencies of the Bible? (There are many. Refer to this list at the Secular Web if you have not realized the Bible is loaded with them)
How do you know which parts of the Old Testament can be disregarded by Christians? If you don't know, then why not?