What is the central idea of the text?
The central idea in this classic sermon is that God not only can and will send Edwards's parishioners to hell in the blink of an eye, but that he has the power and is anxious to punish them for turning their backs on them. Not only that, but he is angry, so angry that he holds the hapless sinner like a spider over a fiery pit, just waiting for the chance to drop it in. The point was to scare the bejeebers out of Edwards's parishioners, and according to reports, it worked.
The scare tactics were designed to get their attention so they'd understand that they could not get to heaven on their own. They had to turn their back on reason and good works (as means to attain eternal life) and confess their sins to God and beg his forgiveness.