The best-supported theme is “pride comes before a fall.” The bachelor’s story shows Bertha being proud of her goodness and her medals, and that pride helps lead to her downfall. Why the others are weaker:

  • Be kind to animals is not the main lesson of the story.
  • Wolves are dangerous is true in the plot, but it is more a detail than the theme.
  • Being good is its own reward does not fit the bachelor’s story as well, since Bertha’s goodness does not save her.

So the clearest answer is: pride comes before a fall.