Luke says that the crowds who had gathered to watch the spectacle returned home beating their breasts. The gesture gives the aftermath of the crucifixion a strongly physical expression of distress.
Ancient mourning and repentance were often communicated through the body as well as through words.
Beating or striking the breast appears in ancient Jewish and Mediterranean contexts as an outward expression of grief, anguish, or remorse. Luke has already used the gesture in the parable of the tax collector, who beats his breast while asking God for mercy.
The Gospel does not tell us that every spectator reached the same theological conclusion. The shared action nevertheless communicates that the crowd departs deeply affected by what it has witnessed.
The custom prevents the final crowd scene from being read as emotionally neutral dispersal. The spectators leave performing a recognized gesture of sorrow.
Luke does not turn them all into disciples, but he does portray the crucifixion as an event that produces public lament and moral unease rather than merely satisfying curiosity about an execution.