Analysis of The House of Life: 97. A Superscription

Look in my face; my name is Might-have-been;
        I am also call'd No-more, Too-late, Farewell;
        Unto thine ear I hold the dead-sea shell
    Cast up thy Life's foam-fretted feet between;
    Unto thine eyes the glass where that is seen
        Which had Life's form and Love's, but by my spell
        Is now a shaken shadow intolerable,
    Of ultimate things unutter'd the frail screen.

Mark me, how still I am! But should there dart
      One moment through thy soul the soft surprise
      Of that wing'd Peace which lulls the breath of sighs,--
  Then shalt thou see me smile, and turn apart
  Thy visage to mine ambush at thy heart
      Sleepless with cold commemorative eyes.