The parallel between this episode in The Adventures of Huckleberry Finn and Romeo and Juliet is fairly obvious. Miss Sophia Grangerford and Harney Shepherdson are the young lovers who come from feuding families. They rendezvous in the church meetings because it is one of the few locations where both families can be in the same location without gunfire. When they meet and elope, the fighting breaks out again, with fatal consequences on both sides.
Huck doesn't understand the idea behind a feud, so Buck explains the history of the conflict. Huck sees no point in the idea; neither does Twain. His writing effectively points out the futility and ridiculous nature of the situation.
A feud is this way. A man has a quarrel with another man, and kills him; then that other man's brother kills him; then the other brothers, on both sides, goes for one another; then the cousins chip in-and by-and-by everybody's killed off, and there ain't no more feud. But it's kind of slow, and takes a long time.