What does Luke 21:18 mean?

Jesus is describing the persecution His followers will face, particularly before the temple is destroyed in AD 70. They will be hounded and arrested by religious leaders. Yet this will give them opportunities to share Jesus with the leaders (Luke 21:12–15). Friends and family will betray them, even to death (Luke 21:16). Now, Jesus gives His followers hope. Although the Jews and Romans, as a group, will hate them, God will protect them (Luke 21:17–19). The comment in this verse seems extreme—but since Jesus has just mentioned these same men dying, it's not meant to be taken out of context.

This verse and the next are difficult to interpret, especially in a hyper-literal modern, Western culture. The phrase "a hair of your head" might be the literary technique of synecdoche: something is mentioned to represent something else, especially using a part to represent the whole. If Jesus is referring to their earthly lives, the promise is problematic. Is Jesus saying that the disciples will face persecution, but they will not be harmed? That can't be; He's already told them some will be killed (Luke 21:16).

The disciples know what Jesus is talking about; or, at least, they soon will (John 16:13). They were there when He told them to take up their cross and that they would save their lives by being willing to give them up. It means they will die to the world but gain eternal life (Matthew 16:24; Luke 9:24–25). He also said they should not fear those who can kill the body but the One who can send the soul to hell (Luke 12:4–5). It is the spiritual, eternal lives that are protected, not their physical lives—and certainly not their hair!