Edwards uses four primary metaphors to develop images of God's wrath. The first compares His wrath to a storm:
There are black clouds of God's wrath now hanging directly over your heads, full of the dreadful storm, and big with thunder; and were it not for the restraining hand of God, it would immediately burst forth upon you.
The second uses the comparison of His anger to the pressure of flood waters behind a dam, building up until they can no longer be contained:
The wrath of God is like great waters that are dammed for the present: they increase more and more, and rise higher and higher, till an outlet is given; and the longer the stream is stopped, the more rapid and mighty is its course, when once it is let loose.
The next metaphor is two-fold: It compares God's wrath to an arrow held in place by the bow of justice:
The bow of God's wrath is bent, and the arrow made ready on the string, and justice bends the arrow at your heart, and strains the bow, and it is nothing but the mere pleasure of God . . . that keeps the arrow one moment from being made drunk with your blood.
The last is perhaps the most famous:
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 . . .
God's mercy, Edwards says, is the only hope we have.
Check out this link for lots of questions on this topic. In fact, this exact question was asked last week...