William Cullen Bryant expressed his views about death most clearly in two of his poems: "Thanatopsis" and "To a Waterfowl." Often associated with the English Romantic poets, Bryant, like them, turned to nature for an understanding of death. In nature, Bryant saw a way of accepting the inevitability of death. Let's start with "Thanatopsis," whose title literally means "a view of death."
This poem begins with praising nature, which has the ability to comfort us with its beauty and vastness:
Of the last bitter hour come like a blight
Over thy spirit . . .
Go forth under the open sky
But in our contemplation of nature, we are also reminded that we will return to Earth and in our death "mix forever with the elements." The consolation comes from the idea that the earth is a wonderful eternal resting place where we will lie down with all the great people of the past and be surrounded by the rivers, woods, and meadows. It is the place to which all must eventually go, and because of this fact we will not be alone:
The speechless babe, and the gray-headed man--
Shall one by one be gathered to thy side
By those, who in their turn shall follow them.
We, then, should not be afraid of death but go to our graves as if we are lying down to begin "pleasant dreams." In this poem, Bryant stresses the fact that becoming one with nature and with all past living things is our solace for death. He does not refer to the afterlife, except obliquely, when he connects dreams and death.
In "To a Waterfowl," Byrant uses the flight of a bird to explain how we should feel about death. This poem has a more religious tone that "Thanatopsis." In the latter poem, Bryant mentions a "Power" that guides the waterfowl to its "summer home, and rest." As he watches the bird's "certain flight" through "the cold, thin atmosphere" until it disappears in the "abyss of heaven," he applies this journey metaphorically to himself. As he walks the long way alone, he knows that there is a power that guides him, that
Will lead my steps aright.
The two poems express similar ideas about death. Nature is a way of understanding and accepting our own mortality. In the first, nature becomes our final peaceful resting place; in the second, nature becomes more of a metaphor that teaches us how we should view death. The second has more religious overtones than the first in its mention of a supernatural power that guides both the bird and the speaker to the heavens.
I have posted two links below that should provide more ideas about Bryant's understanding of death.