The poem
METHOUGHT I saw my late espoused Saint Brought to me like Alcestis from the grave, Whom Joves great Son to her glad Husband gave, Rescu'd from death by force though pale and faint. Mine as whom washt from spot of child-bed taint, Purification in the old Law did save, And such, as yet once more I trust to have Full sight of her in Heaven without restraint, Came vested all in white, pure as her mind: Her face was vail'd, yet to my fancied sight, Love, sweetness, goodness, in her person shin'd So clear, as in no face with more delight. But O as to embrace me she enclin'd I wak'd, she fled, and day brought back my night.
In this poem John Milton visits his deceased wife in a dream. In the last line "I waked, she fled, and day brought back my night" he is saying that as he woke from his sleep it was literally day outside but it was dark to him resembling grief and sadness in his world from the loss of his lover.
Milton 'On his deceased wife'
The poem speaks about the poet Milton being visited in his dream by his deceased second wife, who died four months after giving birth to their first daughter. Milton was blind. He he can see her. As he wakes he returns to his waking reality where he is blind. I would suggest the poem describes an after death contact experience, where the person who has died appears to her husband to reassure and comfort him.
On deceased wife written by johnmilton