In "Sinners in the Hands of an Angry God," what does Edwards consider essential for salvation?

Jonathan Edwards' famous sermon "Sinners in the Hands of an Angry God" is an excellent example of the revivalist movement in churches during the Great Awakening. Grounded in the dominant theology of the day, the Great Awakening introduced an emotional component to the role of the church, using images and prayers to evoke affective responses from the congregation.
Soteriology, or the question of what we must be saved from and how we are saved, is at the heart of Edwards' sermon. He uses vivid imagery to describe Hell, a literal place of eternal torment for those he terms the Wicked. He further describes that the Wicked are literally held, dangling over the pit, by God. It is only the willpower of God, he asserts, that keeps them from falling into Hell at any given moment. People can work to stay healthy, avoid death, profess the best of intentions, even sit in church every Sunday. 
Ultimately, Edwards points toward a covenant of grace between man and God—the idea that God is the ultimate power, but that God created a covenant with mankind through Jesus Christ. God alone has the power of life over death, redemption over sin.
For Edwards, it is merely at his own whim that God keeps man from the pit at any given moment. In order for the pit to be avoided entirely, man must enter fully into the covenant through the mediation of Christ. Intention, good works toward their fellow men, and sitting in church are not enough. Edwards is calling for full-on conversion. It is not simply the mind which must accept and contemplate a concept of covenant and grace. The heart must be fully devoted to Christ. God's restraint from simply throwing them into Hell is a chance to change. 
https://digitalcommons.unl.edu/cgi/viewcontent.cgi?referer=&httpsredir=1&article=1053&context=etas