Huck decides to help Jim because he develops a deep friendship and respect for Jim throughout their journey down the river. Huck sees Jim as a kind and caring person who is often mistreated and underestimated by society due to his status as a slave. Huck also begins to question the morality of the institution of slavery and feels a sense of empathy towards Jim's desire to reunite with his family. Despite the societal expectations and beliefs that dictate that helping a runaway slave is wrong, Huck follows his own conscience and chooses to do what he believes is right, even if it means facing potential consequences.
