The most profound imagery for me in The Voyage of the Dawn Treader is the un-dragonning of Eustace.  After a brief conversation with Aslan, he realizes he has to remove his skin.  He does so only to discover another layer beneath.  This goes on and on until it seems almost hopeless.  Aslan then informs Eustace that he's going to have to let Aslan help him.  Aslan sinks his claws into Eustace's tough dragon skin and tears it from his body.  It's excruciating but exhilarating.  Eustace looks into the pool before him and realizes that he has been set free.  From then on out, Eustace is a changed boy who will come to play important roles in further Narnian stories.

Repentance is exactly the same.  Very often we realize that we need to change and begin to make efforts only to find further difficulties revealed.  It is only when we let the Lord take charge that real change actually begins.