Jonathan Edwards was adamant about convincing his congregation to turn from their wicked ways, so much so that I've considered calling this classic sermon "Parishioners in the Hands of an Angry Preacher."
Part of his method was to thoroughly convince them that God was not only fully capable of committing them to hellfire, but willing to do so and even anxious to get started. Not only that, but Edwards's parishioners deserved eternal damnation.
The natural next step is to paint a persuasive picture of what eternity--a concept literally beyond human understanding--means. It means "you will absolutely despair of ever having any Deliverance, any End, any Mitigation, any Rest at all; you will know certainly that you must wear out long Ages, Millions of Millions of Ages...." If there is anything more horrifying than being dangled like a loathesome insect over the fiery pit of hell by an almighty being who wants to drop you in and believes you deserve it, it is the idea that you will never escape the unspeakable misery of it.
Why, though? His goal was to--quite literally--scare the hell out of them. He used fear (most effectively) to convince his parishioners to rededicate their lives to Christ and to turn their back on the wickedness of Renaissance Enlightenment and reason.