What does John 19:32 mean?

Crucified victims were usually nailed through the wrists and ankles such that pain would be maximized, and blood loss minimized. Infection, exposure, and animals were just as likely to kill the condemned as bleeding to death. The posture of slightly bent knees and outstretched arms meant the chest was naturally pulled open. This made it difficult to exhale. Only by pressing up on the nails, primarily by the feet, could they take a decent breath. Over time, fatigue and shock would make this too difficult, and death by asphyxiation—suffocation—would follow.

To accelerate the process of death, executioners would use a heavy rod to shatter the shin bones. This not only made it impossible to lift one's body. It also added to the shock, blood loss, and general trauma. Even so, this was considered an act of mercy. Without such measures, a victim could take hours, even days, to die.

Since this is a time of religious celebration (John 19:31), the Jewish leaders don't want the city defiled by leaving corpses hanging on the sabbath (Deuteronomy 21:23). The Roman governor isn't going to object to that request, so he approves breaking the legs of these three men (John 19:18). Jesus, however, had been flagellated so badly (John 19:1) that He needed help to carry His cross to the execution site (Matthew 27:32; Mark 15:21; Luke 23:26). By the time this order to break Jesus' legs is given, He is already dead, and there is no reason to carry it out (John 19:33–34).