What does John 8:36 mean?

John 8:36 is one of the most inspirational phrases in all of Scripture. While sin enslaves us (John 8:31–32), true freedom is found only in Christ (John 8:31–32). Sin deceives by promising freedom, when all it does is control and corrupt us. Those who don't have faith in Christ are bound by sin (Romans 6:18), and subject not only to slavery, but to spiritual death (John 3:36). Those who find Christ, the one and only source of spiritual truth (John 8:12), will be "truly" free.

The context of this comment is a discussion about Abraham and the concept of a spiritual "father." The religious leaders of Jerusalem, and their followers, are referred to as "the Jews" in this part of the gospel of John. When Jesus claimed to be doing the will of His "father," these critics responded by laying claim to their ancestry through Abraham. Christ's reply is that biological fatherhood is not as important as spiritual fatherhood. Jesus has just used the example of a household servant, who is not a permanent part of a family, in contrast to a son, who is always guaranteed access to his father (John 4:15–16). This was an analogy to the difference between those who merely know "about" God—including the spiritually obstinate Pharisees—in contrast to those who truly know God because they know Christ (John 8:31–35).

Christ is the real, promised "son" of Abraham (Galatians 3:16). So, the "real" children of Abraham are those who obey God, by accepting Christ (Galatians 3:26). This is the subtext behind the rest of Jesus' dialogue with the crowd.