Simile: "That they were always exposed to destruction; as one that stands or walks in slippery places is always exposed to fall." Here, Edwards uses a simile to explain how precarious is the position of the "wicked unbelieving Israelites." They remain in constant danger of unexpected destruction as a result of their lack of understanding of God. They would be destroyed as a result of their own flaw; they are not the victims of some other power. Emotionally, this comparison focuses on the hopelessness of such a condition while simultaneously assigning blame for one's condition. We are not to sympathize with these individuals when they fall, because they do so as a result of their own ignorance.
Metaphor: "There is no fortress that is any defence from the power of God." In other words, there is nothing a person can do to defend themselves from God's wrath when his appointed time comes. There is no protection from it. Emotionally, this comparison shows us how pointless it is to hide our sins from God, and this goes with the next simile in the list.
Simile: God's enemies "are as great heaps of light chaff before the whirlwind; or large quantities of dry stubble before the devouring flames." Those who oppose God, then, are so incredibly insignificant they are rendered as nothing more than corn husks or tiny seeds to a massive whirlwind or dry tinder against an advancing fire. Emotionally, this comparison makes us feel small, especially when up against God's wishes. We are nothing when we oppose him.
In the sermon, Jonathan Edwards uses many literary devices, and here are six:
1) Imagery, such as: "the dreadful Pit of the glowing Flames of the Wrath of God"
This image is meant to elicit terror in the minds of listeners who envision themselves at the mercy of a vengeful God.
2) Personification, such as, "Hell’s wide gaping Mouth open"
Edwards personifies hell (or makes it beast-like) to unsettle his listeners as they consider being consumed by something demonic and insatiable.
3) Simile, such as: "you would be like the Chaff of the Summer threshing Floor"
This comparison is meant to make listeners understand how inconsequential and worthless they are in God's eyes.
4) Concession, such as, "'Tis true, that Judgment against your evil Works has not been executed hitherto"
This concession is meant to counter the argument that if God were really that angry and bent on destroying them, it would have already happened.
5) Metaphor, such as: "The Bow of God’s Wrath is bent, and the Arrow made ready on the String"
This metaphor is meant to invoke fear; it suggests that God is poised to make an imminent strike.
6) Juxtaposition, such as: "To see so many others feasting, while you are pining and perishing!"
It's a strange strategy, but Edwards seems to be trying to invoke envy for those who are already saved.