Perhaps the thesis statement of this poem can be found in these two lines:
My rest shall be calm in any grave
Where none can call his brother a slave.
The two key themes in the poem, then, are injustice and death, with the poet using the motif of herself still suffering in her grave as an expression of the fact that, as long as there is injustice and slavery, even in death she will not be free to rest.
The poet emphasizes that her request, that her relatives "bury me not in a land of slave," is not such a lofty one. She asks no "monument" and cares not if her grave is "in a lowly plain" or "among earth's humblest graves." The plea that her grave be not trodden upon by "a trembling slave" or "a coffle gang" is actually a very humble one in and of itself; the request for an end to slavery should not be perceived as a lofty goal.
The poet uses the image of herself, unquiet in her coffin, perceiving injustices above, as a vehicle to list a number of atrocities common under slavery, such as "the lash," "babes torn from [a mother's] breast," "bloodhounds seizing their human prey" and girls "bartered" as if they were animals. Slavery, the poem emphasizes, is something so self-evidently atrocious and inhuman that to call an end to it would allow countless others to sleep in peace. For as long as slavery continues, even the dead cannot escape its evils.