What is something unique about the setting of Hawthorne's The Scarlet Letter? How does this characteristic affect the characters?

The Scarlet Letter takes place in Puritan Boston in the middle of the 17th century.  This is a pretty singular time and place in history because the Puritans were a pretty peculiar group.  They settled the Massachusetts Bay Colony in the hopes of creating a society in which the civil and the ecclesiastical were one and the same: religious law was the law.  Further, they believed that the only way the colony would succeed was if everyone conformed to these laws that would regulate correct behavior.  Therefore, Hester Prynne's crime would have been particularly egregious in their eyes because it, in theory, could result in God punishing the entire community.  The first governor, John Winthrop (whose death is actually reported in the story), said that they would be as a "city on a hill"; in other words, the eyes of the whole world would be on them, and so if they succeed, they will be a model for everyone, and if they fail, the whole world will watch them do it.  This community felt a great deal of responsibility, and that makes the setting and characters unique.  It makes the Puritans particularly unmerciful and unsympathetic in regard to Hester; it also makes the Reverend Dimmesdale's sense of responsibility and guilt that much more understandable given the possible ramifications for the entire community.