The sermon "Sinners in the Hands Of an Angry God" basically speaks about an angry god, ready to punish those who dissobbey him, those whoe don´t worship him, a God that even if you don´t feel it, or seems right, it´s coming for you if you don´t do as he says.
Thru the whole sermon the idea of Hell, and the conviction of it´s existence is reminded often, and how disobbeying God is pursuing a hell in life, explains easily how people were convinced by these words, and quickly take action on the witches of salem, which were merely woman that didn´t fit the curretn standards.