Nowadays, we have laws that protect citizens (against rape, murder, kidnapping, and the like), and people suspected of violating these laws will be brought forward before a court and sentenced as a judge and or jury sees fit.
However, the Puritans had extra "laws" against certain ways of dressing, certain ways of practicing Christianity, even how certain daily duties are addressed (for example, they weren't allowed to do ANY work on Sundays). And the Puritans would reinforce these laws by socially ostracizing and/or excommunicating those that did not adhere to these social and spiritual rules. They would also publicly punish or chastise those who would rebel against them.
Buritan law requires a strict adherence to Biblical law. It assumes that all are corrupt and fall short of God's glory. Behavior is tightly regulated. Human nature abhores strict laws, and will do whatever necessary to break them. Puritan laws assure that man will not go outside his nature at the risk of offending God and potentially going to hell.