Ryan H. answered 01/09/20
WPI grad, Engineer with 14 years of experience tutoring
The very short answer is that Puritans believed (as many Christians do) that God was a loving one:
"According to covenant theology, Christ's sacrifice on the cross made possible the covenant of grace, by which those selected by God could be saved. Puritans believed in unconditional election and irresistible grace—God's grace was given freely without condition to the elect and could not be refused."
Bremer, Francis J. (2009). Puritanism: A Very Short Introduction. Oxford University Press. p. 35. ISBN 9780199740871.
In this case, much of the pain and suffering of the world was a direct result of the devil and his minions (demons, witches, etc.) Again this is still a belief that is held and was very common in the 17th century. The Puritans, however, believed that they were especially at-risk. According to one of the prominent minister leaders of the witchcraft trials, Cotton Mather:
“The New-Englanders are a People of God settled in those, which were once the Devil's Territories; and it may easily be supposed that the Devil was exceedingly disturbed, when he perceived such a People here accomplishing the Promise of old made unto our Blessed Jesus, That He should have the Utmost parts of the Earth for his Possession.”
Basically, because the Puritans were a “city upon a hill” and in a new land, they were especially susceptible to the Devil’s work.
There is a lot great reading out there on this, but probably the best is Remarkable Providences by Increase Mather (Cotton’s father and president of Harvard)