I am assuming you are referring to Edwards' most famous sermon, "Sinners in the Hands of an Angry God." In this sermon, Edwards tells his listeners that God has every right to be angry at them and to feel towards them like a person feels towards a spider or other "loathsome insect."
Because of this, people are constantly under threat of having God send them to hell. It is only, to Edwards, God's mercy that keeps this from happening and God could choose to withdraw that mercy at any moment.
In his famous sermon "Sinners in the Hands of an Angry God," Jonathan Edwards uses strong imagery and effective persuasion in an attempt to convince his congregation to repent their sins and turn to God before it is too late and they are sent to hell forever. Edwards truly believes that people are in constant danger of being sent to hell to spend an eternity in terrible pain and anguish. One example out of the text that shows this is the following quote:
"Oh sinner! Consider the fearful danger you are in: It is a great furnace of wrath, a wide and bottomless pit, full of the fire of wrath, that you are held over by the hand of that God, whose wrath is provoked and incensed as much against you, as against many of the damned in hell. You hang by a slender thread, with the flames of divine wrath flashing about it, and ready every moment to singe it, and burn it asunder."
This precarious image of hanging only by a thread creates worry and near panic in the listener. Edwards believes the only reason people haven't already been punished has been that God has been holding them up - but God's patience is wearing thin, and they are in immediate danger.
Another example that illustrates the immediacy of the danger they are in is the metaphor comparing God's wrath to a bow bent with an "arrow made ready." This image of God's wrath as a weapon ready to spring further elicits strong emotional reaction - mainly fear.