The previous post was very lucid in their explanation. I would like to amplify it a bit and take it to a different venue. I think that the Puritans failed to understand and recognize how terrible a reality is when it seeks to pursue a singular notion of the good. The Puritans fled from England because of a social and religious order that was zealous in its pursuit of a singular notion of the good. Within this refusal to acknowledge "the other," lives were ruined and individuals fled in terror. The Witch Trials of Salem represent that same element. The refusal to recognize "the other," plurality in the notion of worship and understanding, coupled with the incessant and irrational pursuit of spiritual perfection resulted in a similar level of terror and abuse of power. The reality presented in the play is two fold: 1) Individuals who pursue singular and oppressive notions of the good do so at the expense of many and 2) These pursuits can be easily twisted and manipulated by those who have self serving agendas.
The Puritans fled to the new continent in order to escape the persecution that they were suffering in regards to how they wanted to practice their religion. They felt that the Church of England was corrupt, and wanted a more pure and clean religion; they broke off and attempted to form their own church. They were persecuted; they were treated as heretics, they were the victims of figurative "witchhunts." They bemoaned the lack of tolerance, acceptance, and rationality shown by those who persecuted them.
Despite the fact that they were the victims of vicious prejudices and irrational fears, despite the fact that they were persecuted and attacked, they did not hesitate to turn and do the same thing to members of their own community. They hunted people down, called them out, accused them of absurd and illogical claims, and even killed them for these paranoid beliefs. They themselves did not take their own advice--they did not purify their intents, they did not treat people with respect, kindness and calm rationality. Unfortunately, the sad instances that occurred in the Salem witch trials showed how human nature is indeed fallible, and subject to the power of greed, hatred, jealousy and envy. I hope that those thoughts helped a bit; good luck!