Life in Puritan New England was harsh and the church wielded great power and influence. While Puritan's had left England in order to practice more freely they were not interested in freedom of all religion. Indeed, they structured the social order around their church.
Peter Marshall and David Manuel explain the influence of the church on a member of society:
"Today, if anyone were threatened with dismissal from church membership, in all probability he would simply laugh, take up his coat, and leave. But it was a different three centuries ago. First, a church covenanted together, then the town formed around it. And under most circumstances, excommunication was a matter of the utmost gravity. It meant that the local body of Christ, after repeatedly trying to bring a sinner to repentance so he or she could receive God's forgiveness, would finally have no choice but to break fellowship with the individual and turn the person over his or her sin. This meant that a person would be under Satan's influence, and for those who know the reality of the Devil, this was a fearsome turn of events indeed. [Marshall, Peter and Manuel, David, The Light and the Glory, (Old Tappan: Fleming H. Revell Co., 1977), p.173].Clergy members, naturally, enjoyed a great influence in the community and many clergy in New England were telling their congregations that the devil was among them in the form of witches. In Salem Village many of those who were executed were also opponents of the town minister Rev. Samuel Parris.
Serious illness in the 17th century often meant certain death. Medical practices were primitive worldwide but even more backward here than in Europe. Infant mortality rates were ?%. Little of known about a number of physical illnesses and even less about mental illness. When faced with an illness they couldn't diagnose, doctors at the time usually proclaimed that the illness was due to the only other "known" at that time--witchcraft.
Many have speculated about the cause of the "strange fits" that affected the young women of Salem who were the chief accusers and trial witnesses-- mental illness, physical illness, and deception.
Arthur Miller in his play The Crucible, sets forth that the fits were lies to cover the fact that the girls were caught doing things forbidden by the church and in the case of Abigail Williams motivated by revenge for a scorned love. In reality, Abigail Williams, a girl of 12, would be unlikely to be romantically scorned by John Proctor. His servant Mary Warren, however, may have had just cause for revenge as transcripts show that he very likely beat her for not working hard enough.
In her paper in Science Magazine, Linda Caporeal [Science Magazine, April 2, 1976] suggests a very real physical illness brought on by ergot poisoning. Ergot is a fungus found naturally in rye in years when weather has been especially wet followed by a very hot period. In the 17th century most people ate rye bread as wheat was far too expensive for all but the wealthiest families. The ergot fungus would be ground into the rye at milling time and eaten by many a villager. Those of small stature, women and children are more susceptible to ergot poisoning. Ergot contains among other things lysergic acid (also a base component of the drug LSD) and symptoms include hallucinations, violent fits, choking, and an itching, crawling or pinching sensation on the skin.
Boyer, Paul and Stephen Nissenbaum in Salem Possessed: The Social Origins of Witchcraft. [Cambridge: Harvard University Press, 1974] provide us with a look at Salem Village and its factions. This book suggests there the town was largely divided into two factions, those who opposed the appointment of Rev. Parris and those who were in favor of it. Those who favored Parris were also the same people who were in control of the trials. Many of those who opposed him were also those who spoke out against the trials. Many of the outspoken who had the nerve to publicly state that either the trials were a sham or even that they did not believe in witches typically found themselves the next accused.