Dwight L. Moody said, "Of one hundred men, one will read the Bible; the ninety-nine will read the Christian."
Brennan Manning said, "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."
Dave Burchett said, "Christians, like physicians, should vow to do no harm. But forgive us, Lord. Because we do."

Good article entitled I am a Christian, and I suck:

Let's face it—to paraphrase Relevant author Matthew P. Turner, we all suck. No way around it—we are all messed up in one way or another when it comes to our relationships with others and how we deal with them. We've all at one time said something utterly stupid, done something hurtful or thought something we know we shouldn't have about a fellow brother or sister in Christ