What does Acts 5:13 mean?

It's unclear what it means that "none of the rest dared join them." It probably means that only the apostles preached on the temple mount while the other Jesus-followers remained in town. This would be consistent with Acts 8:1 wherein many believers flee Jerusalem from Paul's persecution, while the apostles remain. At this time, the apostles enjoy special protection from death—although not from violence, as seen in Acts 5:40—but the new believers do not (Acts 8:3; 26:10). God equips us for the work He gives us, and it's not a sin to bow out where He has not called us.

The transformation of the apostles, however, is significant. When the guards and servants of the chief priests arrested Jesus on the Mount of Olives, the remaining apostles fled into the night (Mark 14:50). Only John boldly followed Jesus into the courtyard of the high priest (John 18:15) and the cross (John 19:26–27). While the women prepared spices for Jesus' burial, the disciples hid in a locked room (John 20:19). Under other circumstances, the Sanhedrin's arrest of Peter and John would have sent the apostles back to Galilee (Acts 4:1–22). But they have received the Holy Spirit (Acts 2:1–4) and prayed with confidence for the courage to speak boldly (Acts 4:23–31).

The other Jesus-followers may stay away, but the public flock to the apostles for healing from illnesses and demon possession (Acts 5:16). Many of them come to a saving faith in Jesus (Acts 5:14). Jesus gave the apostles a mission to be His witnesses (Acts 1:8), and they perform that mission well, even when more serious persecution arises (Acts 5:40). Because of their dedication and courage, we have the gospel message today.