In Chapter XXXI, Huck learns that the duke has captured Jim and sold him; with this act, the ethics of society are in position and Huck views these rules with a dismal outlook. For, after having spent idyllic days and nights with Jim, the escaped slave of Miss Watson, Huck has learned that Jim has feelings just as any other person: he loves Huck and he cries when he fears something has happened to the boy. Indeed, as they have traveled down the river, Jim has acted as a loving father to Huck, counseling him and teaching him of life. His genuine feeling is evidenced in Jim's care and his crying tears of joy when Huck returns to the raft after having been gone so long that Jim has believed him lost. In Chapter XL, Jim refuses to run off to freedom until Tom Sawyer's leg wound is treated; it is at this point that Huck remarks, "I knowed he was white inside."
Much as in this later chapter, in Chapter XXXI, Huck realizes the humanity of Jim, his scruples, and his loyalty as a friend. With his conscience "grinding" Huck writes to Miss Watson about her runaway slave, but cannot harden himself against Jim as he recalls,
...how glad he was when I come back out of the fog; and when I come to him again in the swamp, ...and would always call me honey, and pet me, and do everything he could think of for me, and how good he always was; and...said I was the best friend old Jim ever had in the world, and the only one he's got now....
At this point, Huck looks again at the letter to Miss Watson and tears it up, saying, "All right, then, I'll go to hell." So, Huck rescues Jim from the rapscallions who have stolen him. The irony of Huck's situation is that he performs the most Christian act, his rescuing of Jim. For, although the Widow Douglas and her friend Miss Watson read to Huck from the Bible, they are the lesser Chiristians by having a slave; they are the more the sinners and hypocrites of moral law than Huck himself.