What is the theme in A Valediction: Forbidden Mourning by John Donne?

Death, a theme not uncommon to Donne's writing, is a significant theme in "A Valediction: Forbidding Mourning." In the poem's opening stanza, Donne makes mention of "virtuous men pass[ing] mildly away." He uses this notion of death as a metaphor for his impending departure on a journey that will take him away from his wife for an extended period of time.