In England, the sonnet has often been used to explore themes of transience, death, and immortality. Shelley's "Ye Hasten to the Grave" continues this trend; however, it does so by refocusing attention away from contemplation about death and the afterlife and back toward the pleasures of life in the here-and-now. Shelley partly frames his sonnet as a series of rhetorical questions for the kind of person who seeks to embrace death as part of his or her religious convictions. For such a person, of course, death is not the end of life but rather life's transformation into something new and blissful. In keeping with his atheism, Shelley implies that the belief in such an afterlife is a form of misdirected hope stemming from hubris or conventional thinking (what Shelley calls "the world's livery"). But perhaps worst of all, in seeking out "a refuge in the cavern of grey death," such a person flees not only life's pain but also its pleasure, the "green and pleasant path" that suggests a power and beauty in life's here-and-now.
Even so, it's worth considering that Shelley's poem doesn't actually affirm very much. Even though his position is atheistical, Shelley has given us a poem more interested in asking questions (about life, death, and belief) rather than averring a new doctrine.