Deuteronomy 17:7, commentary and pictures

The law of stoning required the witnesses who accused a person to begin the execution by casting the first stones, and afterward the hands of all the people were to join them. In adultery the husband was responsible for bringing the action, and both guilty parties were to be punished equally, so proceeding against the woman alone was unauthorized. The scribes and Pharisees who brought a woman accused of violating the seventh commandment and asked whether she should be stoned as Moses commanded had themselves led their victim into sin in order to lay a snare.

Jesus appealed to the first-stone requirement against the elders who brought her, showing that their own guilt disqualified them from acting as righteous accusers, so they left without condemning her. By declaring that only the one without sin should cast the first stone, He turned the law upon the plotting elders and exposed the guilty secrets of their own lives. With their robe of pretended holiness torn away they stood guilty and condemned before infinite purity, so they went away one by one, leaving the woman with the pitying Saviour who did not condemn her but charged her to go and abandon sin.

At Stephen's stoning his accusers fulfilled this requirement by casting the first stones in carrying out the death sentence. As they did so they laid their clothes at Saul's feet, and Saul supported the proceedings and consented to Stephen's death. The verse also teaches that evil must be put away from among God's people, with the witnesses who establish the matter acting first followed by the whole community. It applies to the duty of parents and those in authority to purge concealed and cherished sin from the home, the church, and the workplace.