Analysis of Sudden Light

I have been here before,
             But when or how I cannot tell:
         I know the grass beyond the door,
             The sweet keen smell,
     The sighing sound, the lights around the shore.

You have been mine before,--
             How long ago I may not know:
         But just when at that swallow's soar
             Your neck turn'd so,
   Some veil did fall,--I knew it all of yore.

Has this been thus before?
           And shall not thus time's eddying flight
       Still with our lives our love restore
           In death's despite,
   And day and night yield one delight once more?