How did Jonathan Edwards use fear in his sermon to motivate his audience?

Edwards
gave this sermon to his congregation in Enfield, CT, in 1741, during what is known as The Great
Awakening in American religion, a period in which leaders of the church were hoping to
re-instill religious convictions, which they felt were weakening, in their congregations.  It is
almost a shame, by the way, that Edwards is chiefly remembered for this harsh sermon--most of
his writing and his service to the church was much more positive than this sermon
indicates.

The title of the sermon itself--""--is enough to create
fear among people who believe a) that everyone is sinful to some degree and b) that their God is
full of wrath rather than peace and light.  In their belief system, God is not primarily a
merciful being but rather a stern, demanding, angry God who may just as readily toss them into
Hell as let them into Heaven.

We know, for example, from accounts of the
actual sermon that some people were so shaken by Edwards' sermon that they either fainted or had
to leave the church.  That alone tells us how seriously they took the threat articulated by
Edwards.

One of Edwards' most powerful threats is his reminder that

They are already under a sentence of condemnation to hell.  They do
not only justly deserve to be cast down thither, but the sentence . . . of God . . . is gone out
against them. . . . 

Rather than believing they are
destined, if they are good and holy, to go to heaven, every listener understands that he or she,
as a sinful being, is already destined to end up in hell.  We need to keep in mind that hell for
these folks is a physical place full of every kind of horrible torture that one can
imagine.

Edwards uses very concreteto depict the congregation's dangerous
position:

Your wickedness makes you as it were heavy as
lead, and to tend downwards with great weight and pressure towards hell; and if God should let
you go, you would immediately sink. . . .

The imagery
here--lead rolling down and being held up only by God's hand--is meant to convince the
congregation that they are literally full of sin and on the verge, by virtue of their weight, of
dropping into hell--stopped only by God's hand for the moment.  For people who believe in this
angry God, as well as their own sinfulness, this is an incredibly perilous situation over which
they have no control.  Their total lack of control over their fate may be the most powerful and
frightening concepts in Edwards sermon.