I assume you are referring to a thesis statement. One of the aspects that critics praise this poem for is the way that Dickinson in this excellent poem manages to tame or domesticate one of the most powerful and unavoidable of human experiences through the use of a metaphor. In this poem, Death is compared to an unexpected ride in a horse-drawn carriage that takes the speaker ever-onward into "Eternity." This should provide ample scope for a thesis statement discussing the presentation of death and how he is transformed from a scary figure into a kind, polite and unhurried gentleman, "kindly" stopping, not knowing any "haste."
Therefore a good thesis statement you might want to use could be:
Through the use of metaphor Dickinson domesticates death.
Consider how death is presented and how the speaker responds to Death in this poem. Good luck!