to write a letter

a letter arrived God knows when,
and laid by the bedside forgotten,
today on a cleaning spree
I opened it,
the envelope had my name on it
and my address,
but to my surprise no sender's name,
in it was two papers,
one blank,
nothing written,not even a dot,
the other one carried a small note:
"write in blood,
wrench your heart,
squeeze your soul,
delve in pain and then create a poem
full of thought"

and now I sit idle,
knowing not what,
is there an answer to such a letter at all?
addressed to where and to whom?