You've probably had a similar experience with someone you know. I've already recounted the stories of three of my closest friends--one in high school, one in college, and one in seminary--who seemed so dedicated to serving the Lord, and yet all of them eventually turned their backs on Him. One became a dope-smoking rock-concert promoter, and another became a Buddhist. These were not casual acquaintances, but friends at a very close level. I was sure they shared my passion for the true gospel as much as they shared my love for sports. These three young men proved to me that you can profess Christ and not know Him. You can think you're a Christian and later see clearly that you're not; you can certainly deceive other people. Seeing these seemingly intelligent, dedicated, strong Christians abandon their beliefs forced me to think about who is really a Christian and what being a Christian really means. Their actions portrayed them as fellow soldiers of Christ, but in the end their hearts exposed them as traitors. Spiritual defectors are an integral part of the story of Christianity, both past and present. They're in your life and mine, just as they were in Jesus' life. They shouldn't surprise you, defeat you, disappoint you, or cause you to despair. Jesus' insights on spiritual defectors in John 6, and the reaction to His teaching about the issue, give us one of the most compelling and enlightening stories of His ministry. It's worth considering closely.