As devout Calvinists Puritans believed that mankind was utterly depraved. This was thanks to Adam and Eve's original sin, passed down through the generations. For the individual believer, there was absolutely nothing they could do about this; the matter was entirely in God's hands. Only he could make sinners righteous; no one could contribute anything at all to their own salvation; no one could ever know for sure if they were destined for heaven or hell. But they could be certain, through reading Scripture, that they were mired in total depravity.
In "Verses Upon the Burning of our House" Anne Bradstreet illustrates this particular aspect of Calvinist theology. The poem's central metaphor of a burning house is an allusion to the Day of Judgment, when everyone will find out whether they're going to heaven or hell. When she hears the sound of fire, the speaker is reminded that she must prepare for that potentially terrible day when she could well end up being cast down into the flames of hell.
The speaker responds to the ominous crackle of flames with a heartfelt plea to the Almighty to give her strength. Note that Bradstreet does not pray to be spared from hell; that would derogate from God's absolute sovereignty. Instead she pleads for the necessary strength to see her through whatever fate her divine maker has in store for her.