It can be hard to understand why someone who used to be active in church chooses to walk away from the Christian life. These people used to regularly attend Bible studies, sing in the choir, and talk about Christian doctrines. But now they claim to no longer believe Christianity, or they are upset at their church leaders and refuse to attend any longer.
It can be puzzling how people who once were active in their faith can choose to abandon it. Of course, there are many reasons why this occurs. Yet the aged apostle suggested a simple explanation: these people never were true Christians. They were religious. They regularly attended church services. They became familiar with Christian beliefs. They even learned the Christian subculture. But they were never born again.
John suggested that by abandoning God’s people, they finally made manifest what was in their heart. As long as they remained among God’s people, they fooled others into assuming they were spiritually alive. But now that they have gone, it becomes clear that they only had a surface belief, and not a faith that saved and transformed them. They were among us, but they were not of us.