Recently, George Perdikis, one of the founders of the Christian music group Newsboys, announced he is an atheist. On apologetics websites, I commonly encounter comments from people who insist they were once Christians, but are now atheists. What are we to make of such "ex-Christians"? Is it even possible for a Christian to become an atheist?
First, I think it's important to understand what someone means when they say that they used to be a Christian. The word "Christian" has a number of significantly different definitions. Someone could consider themselves a Christian just because they associate themselves with "Christian culture" or are a member of a Christian church. I think it's easy to see that a person who was once a Christian by this definition could easily become an atheist. In fact, a person could be both a Christian and an atheist at the same time, using this definition of Christian.
Another possible definition of a Christian could be someone who accepts the beliefs of Christianity. If Christianity is just intellectual assent of a set a beliefs, then clearly someone could easily change their mind and adopt a new set of beliefs. Someone could believe that the God of Christianity is real at one point in their life, and believe something completely different at another point in life. (Actually, I find that many times people who claim to fall into this category aren't really rejecting the God of the Bible, but an anthropomorphic caricature that really should be rejected. But that's a subject for another blog post.)
Another possible definition of a Christian is the one I generally intend when I use the term: one who has been regenerated and is in a relationship with God. This definition would be synonymous with "born again." (See John 3 if you're not familiar with that term.) It is not logically possible for someone to go from being a born again Christian to being an atheist. It is not consistent for someone to say they believe they were once were in a relationship with God, but now believe God doesn't exist. It would be like someone saying they were once married, until they realized their spouse doesn't exist. If there never was a spouse, then there never was a marriage. Similarly, if God doesn't exist, then it's not logical to claim to have previously had a relationship with him. Someone could reasonably say they once thought they were in a relationship with God but later realized they were wrong, but that's a very different claim. There's a big difference between "I thought I was born again, but was wrong" and "I used to be a born again Christian but now God doesn't exist."
So, how do we deal with an "ex Christian"? The same way we should deal with any unbeliever, model a life of faith and, as appropriate, try to lead them to a relationship with the living God. As Peter said, "Always be prepared to give an answer to everyone who asks you to give the reason for the hope that you have. But do this with gentleness and respect." (1 Peter 3:15)