I recall a DC Talk song (yes, I used to listen to DC Talk) called "What if I Stumble?" The song has an intro that goes like this:
"The greatest single cause of atheism in the world today is Christians who acknowledge Jesus with their lips, then walk out the door and deny Him by their lifestyle. That is what an unbelieving world simply finds unbelievable."
This quote seems to be based on scripture, since you can find a similar theme in Romans 2:24:
"For the name of God is blasphemed among the Gentiles through you, as it is written." (KJV)
"As it is written: 'God's name is blasphemed among the Gentiles because of you.'" (NIV)
I'm not entirely certain that the "greatest single cause" of atheism can be traced to Christian hypocrisy since there are so many other reasons people don't believe in a deity. I, for one, have seen the light and dark side of Christianity and while the prevalence of hypocrites did sour me a bit on religion I can honestly say that it was the paradox of God itself that put the final nail in the coffin.
What Christians need to realize (and what Paul apparently understood nearly 2,000 years ago) is that their definitive, unwavering stance on the existence of God and His claim on morality must absolutely be backed by a compatible lifestyle. You can do so much irreparable damage to your credibility when you don't realize that your religion automatically makes others hold you to a higher standard.
Feel free to use that as your daily devotional.
