How does the persona contrast the couple's love to "Dull sublunary lovers' love"?

In "A Valediction: Forbidding Morning" Donne is seeking to draw a contrast between a love which is limited, earthly, and impermanent ("Dull, sublunary lovers' love") and a higher, more spiritual love, one untouched by the world of space and time and its constant change. "Sublunary" literally means beneath the moon. In the context of the poem, it refers to the world around us, the ordinary everyday world that we all inhabit, including the poem's speaker and his lover.
Sublunary love is impermanent because it is based on the senses ("Whose soul is sense"). Because of that, it cannot endure when lovers are apart and incapable of seeing or touching each other; it cannot tolerate physical separation:

Dull sublunary lovers' love
(Whose soul is sense) cannot admit
Absence, because it doth remove
Those things which elemented it.

A more ideal, more Platonic love, one based on a meeting of minds, is not simply more enduring; it is permanent:


But we by a love so much refined,
That our selves know not what it is,
Inter-assured of the mind,
Care less, eyes, lips, and hands to miss.



Because such love is not dependent on physical proximity, it continues to last even when lovers are not together. In this higher love which the speaker shares with his lover, their souls are as one; they are soul mates, as we might say. So although the lovers can be apart on a physical level, they will always be together in both spirit and intellect:


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



Donne uses the conceit—an elaborate metaphor—of a pair of compasses to describe the lovers' ultimate unity:


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 the other do.



Try to imagine putting two compasses together. The needle point of both would move in tandem despite their being physically separate. This is what the higher spiritual love of the speaker and his lover is like. The compasses, like the lovers' souls, obey a higher law that transcends the world of the senses. They are drawn together and both point in the same direction.
https://www.poetryfoundation.org/poems/44131/a-valediction-forbidding-mourning