"Sinners in the Hands of an Angry God" is Edwards's most famous sermon, which he delivered on a visit to the congregation at Enfield, Conneticut, in 1741. The "natural men" whom Edwards tries to awaken and persuade through fear are those people in the congregation who have not been "born again"; that is, they have not accepted Christ as their savior. Edwards's methods in this sermon were influenced by the work of the English philosopher John Locke, who believed that everthing that people know comes from experience, and he emphasized that understanding and feeling were two separate kinds of knowledge.
Thus, Edwards uses the word fire and the metaphor the flames of wrath frequently to create fear in the minds and hearts of the congregation. His use of other words such as abominable and God's abhorrence of those who have not been "born again" not only generates fear, but it also causes the congregation to repent their ungodly ways. Thus, fear and repentance are the emotions that Edwards seeks to evoke, so the congregation will return to God after hearing his sermon.
When you read this sermon and come upon such statements as these:
There is nothing that keeps wicked men at any one moment out of hell, but the mere pleasure of God
There is no want of power in God to cast wicked men into hell at any moment
The devil stands ready to fall upon them [sinners], and seize them as his own, at what moment God shall permit him
I would have to say that Edwards is appealing to the basic emotion of fear and to the secondary emotion of remorse.
In this fiery sermon, Edwards was trying to fire up (no pun intended) a luke-warm audience who, he felt, did not appreciate or understand the extent of God's grace in forgiving mankind for his sins. So, in this sermon he first begins by trying to scare the congregation into recognizing that they are vile sinners in need of repentence and forgiveness. Then, when he points out their extreme debasement, he gets into the part that in spite of the horror of sin that all men possess as part of their sin nature, God because of his all-encompassing love for man, provided the means to save man from his sin. The only requirement is that man have faith.
Edwards' choice in appealing to fear was considered "appropriate" for the time in which it was given - Puritan New England. Edwards was quite concerned that there might have been unsaved people in his audience. Although some people can be scared into salvation, most people are attracted to saving faith by focusing on God's love for man, so in modern times, people read this sermon from a different perspective. If one understands that Edwards was a passionate minister that cared about what happened to his congregation if they did not come to faith, however, then his choice is understandably appropriate to achieve his goals. Better to be scared into heaven than coddled into hell.