In the first two lines of "Because I could not stop for Death—" what adverb defines Death's actions?

"Kindly"

Emily Dickinson's "Because I could not stop for Death," composed around 1863, envisions one's death as a carriage ride to immortality. Death collects the poem's persona, or speaker, and they pass by a school and field before arriving at their destination: the persona's grave. 

The poem's title and first two lines personify death as a gentleman caller: "Because I could not stop for Death - / He kindly stopped for me" (1,2). Typically, titles of poems follow strict rules of capitalization; yet here, Dickinson only capitalizes the first word and "Death." Since "Death" is capitalized, and the poem refers to death with the subject pronoun "he," the concept of death becomes personified. The poem describes Death as "kindly," and as possessing "civility" (2,8). Death is not imagined as the grim, scythe-wielding villain most regard it to be, but instead as a gentle, well-mannered carriage driver. For Dickinson, then, death itself is not a somber event, but a benign force that gently conveys us to the afterlife.