A wife at daybreak I shall be,
East and Victory
East = sunrise = marriage, but also death. Dickinson uses 'East' elsewhere for heaven. The victory might not be what it seems.
angels bustle
Wedding guests or death angels? 'Bustle' is domestic, mundane—angels preparing for her arrival in heaven, not at an altar.
Future climbs
Her 'Future' is personified as someone approaching her room. Could be a groom, could be death—both climb stairs to claim her.
Eternity, I'm coming, Sir
She addresses Eternity (death/God) with the same formal 'Sir' she used for powerful men in letters. This isn't a human groom.
seen that face before
Final twist: she recognizes this 'Master.' Death/God isn't a stranger but someone she's already encountered, perhaps in visions or poems.