What narrative purpose does Huck's eavesdropping on the conversation between kings and the duke serve

Huck overhears the The Duke and King talking about their con-job. Huck has continued to mature through the story but has not yet taken sides or definitive steps to act on his moral conscience. Huck decides to thwart their plan to steal the $6000 from Wilks sisters. The narrative purpose is to show Huck as a young man of action rather than a playful boy. Earlier (ch.24) Huck says the sight of the two con-men makes him ashamed to be part of the human race. Huck finally becomes an agent of positive change.