Why should the parting couple "melt" and"make no noise"?

The speaker tries to suggest that death should not cause the couple to be sad or to mourn because their "two souls [...] are one," and though the speaker "must go," the parting is not like "A breach, but an expansion, / Like gold to airy thinness beat." In other words, then, it is not that the couple's souls are being parted from one another but rather that their one, shared soul is being stretched, grown bigger in order to include more space as he travels away from her. It is like gold pounded flat: the gold is the same but just changes shape. The speaker wants his lover not to mourn or cry (to "make no noise") for the loss of him because he does not perceive his death as a loss. Instead, he wants her to think of the two of them as being parts of a compass: one part stays standing erect in the center while the other part circles around it. Both parts move, though one part moves more than the other, though her "firmness makes [his] circle just, / And makes [him] end where [he began]." He knows where to return because she anchors him.