Sonnet: 'As from the darkening gloom a silver dove
bedight
Archaic past participle meaning 'adorned' or 'arrayed.' Keats uses deliberately old-fashioned religious diction throughout—this reads like a 17th-century devotional poem, not 1816 Romanticism.
immortal quire
Archaic spelling of 'choir'—the company of angels singing in heaven. The dead person either joins the heavenly chorus or becomes an angel carrying messages from God.
cleav'st the air
'Cleave' means to split or cut through. The soul either sings with angels or flies as a messenger angel. The elision ('cleav'st') maintains the iambic pentameter.
Wherefore does any grief
The turn: if the dead are in paradise doing glorious work, why grieve at all? 'Wherefore' means 'why,' not 'where'—he's questioning the logic of mourning.