In Shakespeares Sonnet 146, there are three registers which can all be related through the choice of the word "thrall" in the second line. One register pertains to the spiritual conflict between the body and soul, another to a contract between the body and soul, and the last register of war between the powers of body and soul. For the missing words in line two, having the spirit "thrall to" the "sinful earth" provides a link whereby all the registers can be combined. Thrall suits all three registers the best. Combining the three registers makes the sonnet much clearer.
Being able to find and relate all the registers can be difficult. Shakespeare addresses his "poor soul" in the first line of his sonnet, which is part of the first register. The soul can have both a temporal and a spiritual meaning. In the context of how he ends the phrase by referring to sin and addressing the body as "sinful earth," the reader now can see this spiritual register. If the soul were to have a spiritual relation to the body it would be a part of the body but exist beyond. At this moment where Shakespeare addresses his soul, it is enslaved to, or "thrall to" the encasement, the "fading mansion," of his body (6). The words in the second line are necessary to understand how Shakespeare meant the soul to be related to the body. As the sonnet continues, it becomes more obvious that the soul is the lesser entity than the body, and that the eventual freedom of the soul from the body is important.
Later in the sonnet the soul gains its freedom because it is commanded to "live thou upon thy servants loss" (9) and this introduces the second register. The soul has a contract, a "short lease" with the body, to be a part of it and to serve it (5). The soul is enslaved. The sonnet shows how the soul is in servitude through the fact that the soul does not inherit what is left over when the flesh of the body dies. That is left to the "inheritors of this excess" of the "large cost" that "upon thy fading mansion spend," the worms (5-7). This contract is between the body that rules through life and the soul that eventually rules after death. The soul gains its freedom by the end of the contract and the death of the body.
Before the soul can gain its freedom a struggle exists. The sonnet suggests a civil battle between the soul and the body over this control that the body has over the soul during life. "These rebel powers" is what leads the reader to believe it is a civil war, one party rebelling against the larger power (2). The soul is the rebellious power, rebelling against the body. It becomes a war when these powers "that thee array," comes at the end of line. The soul is figuratively being dressed for battle against the body. The soul is held captive to or "thrall to" the body and forced to "suffer dearth" or the glory and splendor that comes at the expense of the war and of the soul (3).
Though there is an expense, triumph does come. The soul, by the end of the sonnet, has triumphed both over the soul and over death: "Death once dead, theres no more dying then" (14). Though the soul is enslaved, brought into bondage, and held captive by the body, it does eventually gain its freedom. Sonnet 146, through these three registers, explores the relation between the soul and the body, an exploration understood better through by the words "thrall to" being inserted into the first two lines.