Rhetorical devices are elements that an author or speaker will use to persuade his or her audience. The person delivering the message should, ideally, use logos, pathos, and ethos to persuade an audience.
Edwards easily handles the ethos portion of the rhetorical situation. As a minister, his audience is much more willing to take his words about God, scripture, and faith at face value. While Edwards doesn't avoid using logos in "Sinners in the Hands of an Angry God," frequently quoting scripture to build his argument, he predominantly appeals to pathos into the sermon. His tone and usage of imagery are largely meant to elicit an emotional response from his audience.
Edwards appeals to pathos in a variety of ways, including second-person addresses directed to his audience ("Your wickedness makes you as it were heavy as lead") and vivid diction inspired by the Bible ("the devil is waiting for them, hell is gaping for them, the flames gather and flash about them"). These rhetorical choices seize and sustain the audience's attention.
Perhaps Edwards's most notable device is his use of figurative language, including metaphors and similes. One compelling metaphor that Edwards uses is when he describes the danger that his audience is in. They deserve the fires of hell, and they are in great danger of experiencing the fires of hell. Edwards conveys that idea by comparing their situation to being held over a fiery furnace.
O sinner! Consider the fearful danger you are in: it is a great furnace of wrath, a wide and bottomless pit, full of the fire of wrath, that you are held over in the hand of that God, whose wrath is provoked and incensed as much against you, as against many of the damned in hell.
Another famous image in this sermon is that of the spider being dangled over a fire. It is a great simile, and it very effectively creates fear and tension in the audience.
The God that holds you over the pit of hell, much as one holds a spider, or some loathsome insect over the fire, abhors you, and is dreadfully provoked.
That simile is meant to draw an immediate emotional response out of the audience, forcing them to imagine themselves from the perspective of a pitiless God.