Misapprehension

Out of my heart, one day, I wrote a song,
  With my heart's blood imbued,
  Instinct with passion, tremulously strong,
  With grief subdued;
  Breathing a fortitude
  Pain-bought.
  And one who claimed much love for what I wrought,
  Read and considered it,
  And spoke:
  "Ay, brother,--'t is well writ,
  But where's the joke?"