before the Son of Man comes: Scholars disagree on whether this refers to Christ's second coming for his church or an earlier judgment, specifically the destruction of Jerusalem in AD 70 (see 16:28).
you will not reach: Jesus might mean “before you have fled through all the towns” or “before you have spread the gospel in all the towns.” The focus on persecution in the context (see 10:17–39) supports the first idea. It suggests the towns were like cities of refuge (Numbers 35:9–32). This emphasizes how widely they will reject the message. It means “not until the whole nation has expelled you.”