Emily Dickinson was a renowned Romantic poet. Her attention to images of nature brought forth one of the characteristics typically found in the genre. Therefore, the fact that she included ideas related to nature were no surprise.
In regards to her poem, "Because I could not stop for Death-," the images of nature resound throughout the lines. In the third stanza, "grazing grain" and the "setting sun" both depict images of nature. The fifth stanza even refers to death, by depicting a rising of the ground (signifying a grave).
The poem, itself, reflects the idea that one should not fear death, given it is an integral part of life. The speaker does not question getting into the carriage with Death. The ride from youth (signified by the passing of the school yard) to the grave (signified by the mound of ground at the end) is rather relaxing. Coincidentally, the fact that Immortality is in the carriage may add to the speaker's lack of fearing death--given, for some, death only signifies the end of one life (the mortal one) and the beginning of another (the immortal one).
One poignant poetic device included in the poem, personification, makes Death less frightening. By personifying death, one need not fear it--it is given a face, a body, and the ability to act in human ways (being kind, civil, and not hasty). In the end, the speaker's travels with Death have been anything but fearful. The drive has been leisurely and quiet. Death has treated the speaker with courtesy and civility. There has been reason to fear death at all.