To make sense of the last lines, it might be proper to put them in thematic context of the first lines. This somewhat cryptic poem manages to succinctly weave together three different themes: women’s rights; slavery; and (in terms of Christian theology) the doctrine of man. Some external evidence would be the time period in which Dickinson lived (1830-1886) in which we have the parallel struggles of Abolition and the Women’s rights movement (and/or Women’s Suffrage) couched in the predominantly Judeo-Christian culture in which core values were largely sustained by belief in the Bible as the “Word of God.”
The line afraid to “own a body” possibly alludes to the repulsive notion of slavery—that no one should own someone else’s body. On that same note—bearing in mind Women’s Rights—women are likewise no one’s property. This idea challenges “old school” notions of women (historically) being chattel and, in some ways, were not much better off than slaves. They were not even allowed to own property in a world “ruled by men."
The next line “own a Soul” turns the theme of the poem from mere challenges of distinctiveness and freedom into Christian theology (while not negating the values of the first line). Biblical, Judeo-Christian theology seems to teach that human beings are comprised of at least two parts: body and soul—(some might say body, soul, and spirit—see I Thessalonians 5:23)—but at least body and soul. Both body and soul (and spirit) are the property of God and therefore “precarious Property” (line 3) denoting our body and souls belong to no one but God. In terms of abolition and women’s rights, this signifies that human beings are free agents—to be “owned” by no one as “possession [is] not optional.”
The language of property continues with the words “Double Estate” (line 5) denoting the dual nature of humans (body and soul) that is “entailed at pleasure” (line 5)—which is to say bestowed upon us all (us “unsuspecting Heirs” (line 6)) presumably by the will of God. What are we “Heirs” of then? According to the Bible, “heirs of God, and joint-heirs with Christ” (of the Kingdom of God)(Romans 8:17, KJV). Christians as “heirs” is a major theme in the New Testament; (see also: Rm 4:14; Ga 3:29; Titus 3:7; He 1:14; etc.).
The vernacular of property continues with “Duke” (line 7) notably a male title of a property owner as opposed to “duchess”—(again denoting a predominantly male society in which Dickinson lives)—and in context serves to resonate a sardonic tone; perhaps from a person who has good reason to be critical of her society. In any case, the Duke presides over his property for this “moment of Deathlessness”—which is to say life is short and any property one might own will not be his (or hers) for long.
The syntactically challenging enjambment of the last line “And God, for a frontier” denotes that in the end, it is God to whom we all belong and ultimately to his “frontier” (line 8). Again, Dickinson employs the vernacular of land to describe, presumably, the afterlife as a “frontier”—arguably imagery of early America—denoting vastness, wild, and free—unowned by anyone (save God)—where we will all be free.
Sources
Kupsh, Charlotte. “The Uncomfortable Self: Emily Dickinson’s Reflections on Consciousness.” Criterion: A Journal of Literary Criticism, Volume 11
Issue 1 Volume 11, Issue 1, Winter 2018, pp. 49-61.
The Holy Bible, Authorized King James Version, Thomas Nelson, 1972.