Donne's speaker begins with the very weird metaphor of an old man dying. Romantic, right? He says that the parting between him and his wife should be like the gentle death of an old man—you can't even tell when he's stopped breathing. You had us at 'dead guy,' John.
Then he shifts gears and compares shallow love to earthquakes that make a big scene and cause a big fuss, but don't have tremendous lasting effects. On the contrary, his love is like the unnoticed, subtle movements of the stars and planets that control the fates of every person (well, according to popular belief). That super-handsy couple can't stand to be apart because their love is based solely on physical contact, but the love he has can stretch any distance because the pair share one soul. Now he's turning on that old Donne charm.
To further prove the greatness of their love, he gives his last metaphor: a mathematical compass—because nothing says sex appeal like mathematical apparatus. But he says that he and his wife are like a compass when drawing a circle. One foot of the compass (Donne) goes way out and travels around, while the other (his wife) stays planted at home and leans after it. But those two compass feet are part of one unit and will always end up back together. And we give props to anyone that can drop the microphone with that as a closing image.