I would argue that the overwhelming central message of this excellent poem regards the love that the speaker has for his wife, and the way that their years together have forged a kind of connection that is more spirtual than physical. The way in which the poem presents their love as being a force that cannot be separated, even by death itself, is incredibly moving, and forces us to think about the nature of love and how it endures even in the face of darkness and death. One of the most striking and beautiful images of this poem helps us to understand the special nature of the love between the speaker and his wife, who possess a love that is "so much refined":
If they be two, they are two so
As stiff twin compasses are two,
Thy soul the fixed foot, makes no show
To move, but doth, if th'other do.
By describing their souls as being like the two feet of a compass, the speaker makes it clear of the kind of union that characterises their relationship. Even when the two feet are apart and separate, they are united, and this unity is shown in the way that, when the other foot "far doth roam," the foot that remains in one place "leans, and hearkens after it / And grows erect, as that comes home." The overwhelming message of this poem therefore concerns a love that is so based in unity and trust that even death itself cannot separate the two souls of the speaker and his wife.