"Thanatopsis" zooms way, way out. It starts out talking about a single person, someone who is going to die soon. Just as soon as we’ve got our heads around that, though, we start hearing about all the people who have ever died since the beginning of time. The speaker isn’t just talking about today. He wants us to think about huge, infinite spans of time, way beyond our own lives. It’s a little hard to tell if that’s supposed to make us feel better about death, but it sure is a wild ride.
"Thanatopsis" tries to take away the pain of thoughts of death by changing the way we think about time. The poem expands our sense of time so much that our own fears begin to seem insignificant.
Bryant asks us to imagine that we are about to die as a way of clarifying and focusing the big, cosmic concepts in the poem.