Why is Jim valuable to the doctor and Silver?

At first, Livesey scolds Jim for running off and leaving the group, especially because he did so at a time when the captain was wounded. Jim begins to cry and tells the doctor that he is not afraid to die, he is only afraid of torture. The doctor then tries to persuade Jim to run away, but the boy refuses because he has given his word to Silver and trusts him. Jim then tells the doctor about his adventures, finishing with the good news that the Hispaniola is beached at the North Inlet. Humbly, the doctor says that Jim ahs saved their lives at every point and that somehow they will find a way to save Jim. So, in Silver's control, Jim is currency while Jim is almost family to the Doctor.