How does Anne Sexton use imagery in Courage?

Examples of Imagery:

Your courage was a small coal
that you kept swallowing.
If your buddy saved you
and died himself in so doing,
then his courage was not courage,
it was love; love as simple as shaving soap.

Later,
if you have endured a great despair,
then you did it alone,
getting a transfusion from the fire,
picking the scabs off your heart,
then wringing it out like a sock.