A Valediction Forbidding Mourning - the final four verses

This is so clever, it makes my heart sing!

Having set things up very nicely, Mr Donne now compares the parting that he and his lover (who are so in love that they are one soul) must endure to beaten gold - which does not break but expands...does not change in volume but broadens.

Our two souls therefore, which are one,
Though I must go, endure not yet
A breach, but an expansion,
Like gold to aery thinness beat.

Then, being the brilliant metaphysicist that he is, he uses a simple tool - the draughtsman's compass - to illustrate further the connectedness and interdependence of he and his lover:

If they be two, they are two so
As stiff twin compasses are two ;
Thy soul, the fix'd foot, makes no show
To move, but doth, if th' other do.

And though it in the centre sit,
Yet, when the other far doth roam,
It leans, and hearkens after it,
And grows erect, as that comes home.

Such wilt thou be to me, who must,
Like th' other foot, obliquely run ;
Thy firmness makes my circle just,
And makes me end where I begun.

Can't you just see that compass, the fixed foot - ever stable and in one place, yet leaning toward the movement of the other foot? Can you also see the moving foot, 'obliquely' running, but made sure and certain by the stability of the fixed foot, and - ultimately - finishing up 'where I begun'?

I love it!