I would look at the part where the speaker is talking about how dead people become one with nature. I think that this is really the heart of the poem -- it is where Bryant is portraying the universe as living and cyclical.
In that part, for example, he talks about the oak tree sending roots down through the dead person. He talks about the dead person then being as one with the "patriarchs" of the "infant" world. The person dies, but he goes back and helps to renew the world.