I know it is a bit on the simplistic side, but I think the title sets forth Edwards' purpose in a fairly succinct and direct manner. The idea that at this particular moment, the force of the divine is disappointed and filled with wrath towards human beings is something conveyed in the title. The idea that human action has caused this state of affairs and there has to be a sense of atonement is also conveyed in the title. The notion that all of the Colonists are "sinners in the hands of an angry god" help to bring to light Edwards' belief that the embrace of materialism and economic notions of the good at the hands of spiritual pursuits is fairly well brought out with the title of his work. Certainly, there are images- the bow of god's anger is bent and aimed at all humanity- that Edwards employs, but they all arise from this particular title and point which apparently was crying to be made.
Here is the most direct statement I can find in the entire sermon in terms of specifically stating his purpose:
I am dwelling on this awful subject so that unsaved people in this congregation might be awakened.
As you may know, this sermon is studied because of its great metaphors, similes, persuasive techniques and ability to demonstrate the Puritan belief system. The entire sermon demostrates the wrath and grace of God. About 90% focuses on wrath, 10% on grace at the end. He does a great job demonstrating people are not much on their own until they accept Christ, then all is forgiven.
Here's another pretty direct statement as a good second place for you:
How awful is the condition of those who are daily and hourly in danger of this great wrath and infinite misery. But this is the dismal case of every soul in this congregation that has not been born again, however moral and strict, sober and religious they otherwise might be.
Hope that helps.
"His anger is as great toward them as to those that are actually suffering the execurions of the fierceness of His wrath in hell. . ."