Final answer:
The challenge presented by the film is the importance of self-reflection and self-discovery, encouraging individuals to understand and change themselves before trying to change the world.
Step-by-step explanation:
The challenge presented by the film to all people, including Wilberforce himself, is the importance of self-reflection and self-discovery. The Butler tells Wilberforce that it is a sad state for a man to know the world and not himself first. This implies that before trying to change the world, one should understand and change themselves. This message encourages individuals to reflect on their own beliefs, values, and actions in order to make positive changes in themselves and the world around them.