Rhetorical strategies are persuasive devices. They differ from literary devices, which can be persuasive, but primarily add extra value to words beyond the literal.
Edwards's chief rhetorical strategy is fear. He wants his listeners (his congregation) to repent and turn back to Christ, and he believes that building up their fear of eternal damnation is the best way to achieve this goal.
He therefore uses the literary device of imagery--describing with the five senses of sight, sound, taste, touch, and smell--to maximize his congregation's horror at the idea of going to hell. He does this by making hell seem very near to us. It is not "out there" as a place we might encounter in a distant time, but a present danger.
Edwards, for example, uses the image of a rickety, broken bridge and says this is what our life is, right now. We are walking across this bridge unseeing, with broken slats beneath our feet, and at any time could plunge into the flames of hell below us. This might not happen tomorrow, but right now. The only thing that can save us is faith in Jesus Christ. We have to repent of our sins immediately and turn to Christ's salvation.
Edwards uses many rhetorical devices in "Sinners in the Hands of an Angry God" to convince his listeners to repent and join the Great Awakening. For example, he uses several figures of speech, including metaphors. In one example, he compares God's enemies to "Heaps of light Chaff before the Whirlwind; or large Quantities of dry Stubble before devouring Flames." In other words, God's enemies are as weak and helpless as pieces of wheat before a large wind or dry tinder before a fire. Metaphors create visual images in his audience's mind and help emphasize his message.
Edwards also makes use of the repetition of words and phrases to drive home his ideas. For example, he writes, "As he that walks in slippery Places is every Moment liable to fall; he can’t foresee one Moment whether he shall stand or fall the next; and when he does fall, he falls at once, without Warning." These lines repeat the word "fall" to emphasize that one who is not saved by God is liable to fall into damnation at any moment, and the repetition of this word serves to emphasize the precarious nature of the unredeemed.
He also uses repeated sounds, or alliteration (starting words that are close together with the same sounds). An example is "Fire is made ready, the Furnace is now hot, ready to receive them, the Flames do now rage and glow." The repeated use of the "f" sound at the beginning of words drives home the vision of a fire-filled furnace with flames that awaits the sinner.
Finally, Edwards uses an appeal to the audience's emotions through techniques such as cataplexis, which is predicting doom for sinners. For example, Edwards says, "And you Children that are unconverted, don’t you know that you are going down to Hell, to bear the dreadful Wrath of that God that is now angry with you every Day, and every Night." He prophecies damnation for those who do not join his movement.