“The greatest single cause of atheism in the world today is Christians: who acknowledge Jesus with their lips, walk out the door, and deny Him by their lifestyle. That is what an unbelieving world simply finds unbelievable.” -Brennan Manning
This may be totally anecdotal but most of the people I’ve encountered who have sworn off the faith have done so because of what they have seen from us. No, we’re not called to be perfect and even if we were we still would fall short. But sometimes we’re not even trying. Maybe even a lot of times.
We are called not to perfection but to radiate the light. If we want to secure an atheist in their faith we simply need to show them the darkness.