As we were on the plane, flying home from the Dominican Republic, a friend of mine (William) got into a conversation with a Polish man who currently lives in North Carolina. William asked him if he knew for sure if he would go to heaven when he died. The man said he didn't know for sure, but would like to. So, William proceeded to share the gospel with him.
An hour later, they had run down all sort of religious and philosophical rabbit trails. That's when I joined the conversation. We did our best to try to get back to the main point, but by this time he was trying to convince us that he was a Christian. However, he clearly did not believe what the Bible teaches about salvation. I have had similar conversations in which someone claimed to be a Christian and did not believe biblical teaching on salvation, and there seemed to be no way to break through their mind set.
Soon after we returned home, I discovered this video by Tim Keller, "Questions for Sleepy and Nominal Christians." I was particularly struck by the title of the article about the video on churchleaders.com: Three Questions Fake Christians Can't Answer. These are very helpful ideas for talking with people to claim to be Christians but don't seem to understand it or don't seem to be walking it.