"Sinners in the Hands of an Angry God" by Jonathan Edwards is considered one of the most important works growing out of a movement called the Great Awakening, a strongly Calvinist movement that developed in the 1730s in the United States, based on the notion that the the spirit of the United States had become too secular and religion too liberal and lax.
The first important theme in the sermon is that of humans' complete depravity. Humanity, according to Edwards and his fellow Calvinists, is by its nature and by its embodiment in sinful flesh, completely and utterly depraved. Sinfulness makes humanity loathsome in the eyes of God.
From this stems the theme that humans cannot achieve salvation of their own works or will, but that they are totally dependent on God's grace or mercy.
The next theme is the notion of the fires of eternal punishment which await the sinner. Thus this is sometimes called a "hellfire and brimstone" sermon, meaning that it urges sinners to repent by drawing vivid pictures of the torments awaiting them if they are not saved by God.