Why is it important that he must pick the pearl from “dying flesh” in order to get it?

I think this has something to do with the hand Kino had smashed on the doctor's gate. His hand was torn and discolored; its flesh discolored by the sea, and it was with this hand that he opened the oyster and removed from the dying flesh that concealed the pearl. In this context we can see the parallel between the dying flesh of his hopelessness (his interaction with the doctor), and his subsequent moment of triumph and great hope.