Roethke's "Elegy for Jane" is, well, an elegy (a poem reflecting on someone's death). In short, the poem's title and subtitle let us know that things ended badly for Jane and that her demise was due, in no small part, to her inability to stay on a horse.
The speaker begins by remembering Jane—connecting her physical characteristics and personality traits to a variety of natural imagery. He goes right on remembering throughout the poem's first three stanzas.
In the poem's fourth and final stanza, the speaker wishes he could bring Jane back, to wake her from the eternal sleep of death. Spoiler Alert: He can't. The poem ends with the speaker's declaration of platonic love for his fallen student and we are left to consider the impact of one human life on another outside the context of romantic or familial love.