Every 80 years or so, a piece of literature comes along that transcends genres. The thing that defines a truly great story is that it has a plot rich enough to resonate though time, but simple enough that it can serve as a lens that becomes an allegory for whatever issue is most important to you in the moment.
Read most simply, The Story of Ferdinand is a lesson on the value of passivism. Ferdinand is a bull living in Spain that has the bad luck of being stung by a bee at the exact moment that scouts from the bull fights come to his pasture. They are impressed by his spunk and select him for the ring.
On the day of the fight, Ferdinand spots a flower in the ring and gets so distracted that he doesn't notice the parade of people trying to goad him into fighting. Without a willing combatant, the fight organizers are thwarted and the audience doesn't get their bloody show.
But here's the thing.... Ferdinand is a bull who socially, is a little off signal from his peers. His life is changed when a disruptive sensory experience (being stung by a bee) creates a misperception of him by the authority. When he gets to the fight ring, Ferdinand is so hyper focused on his idiosyncratic interest (flowers) that he misses out on the social cues around him (the fight organizers trying to get him angry).
The beautiful and timeless message of this story is that being a little different is what makes us special and lovable.