The title, "Sublimation," is a clue to the whole poem. In chemistry, it means a solid turning straight into gas, skipping the liquid stage. In everyday language, it can also mean turning a raw desire into something higher or more refined. Both senses fit here.
The speaker describes a love that cannot be expressed through touch. Instead of reaching out to hold someone, the hand "may become a wing," as if longing, denied its usual outlet, lifts into something lighter and freer. The word "may" keeps this tentative, a possibility rather than a certainty.
The second couplet shifts to "the company of the dead," which suggests grief or loss, though the poem doesn't say whose. Strangely, the speaker finds the light "ravishing" there, not bleak. The mood is quiet and hushed, but not despairing. Loss seems to sharpen the speaker's attention, so that absence becomes a source of beauty and a kind of transcendence.