Tom joins a youth group called the Cadets of Temperance because he admires their outfits, which include a red sash. To join the group he promises never to drink, chew tobacco, or swear, which makes him want to do all three.
Tom joins the cadets not because he believes in their moral stand but because he likes how being a part of the group makes him look. While, for Tom, this is literal -- he likes their outfits -- many adults also join groups for the public esteem being a member of those groups provides.
After less than two days as a member of the group, Tome decides that he will remain as a Cadet until the ailing Judge Frazer passes away. But not long after the judge recovers, and Tom quits anyway. Then the judge dies. Tom vows never to trust such a man again, because the Cadets got to march in his funeral, looking great.
Tom cares more about getting to look good while marching in the funeral than about the fact that a man has died. Though he is maturing, Tom is still just a kid and does not understand the gravity of death.
Once he has quit the cadets, Tom ceases to interested in drinking, smoking, or swearing. In fact, he finds that he's bored without school to go to.
He also misses Becky, who is with her parents in Constantinople.
Tom feels a sincere attachment to Becky..
Soon after, Tom gets the measles. He is bedridden for two miserable weeks. On the day he is finally fully recovered, he heads out of the house hoping to misbehave. However, he discovers that a religious revival has hit the town, including his friends. All of his friends, even Huck, are now preoccupied with the bible and its teachings. Tom feels lonely.
Tom's illness leaves him in solitude, which is the worst form of torture for him. Through the "religious revival," Twain satirizes the integrity of religious devotion, portraying it as a fad that can pass through a town..
That night a terrible storm rages. Tome hides under his sheets, convinced that God has created the storm with the sole purpose of destroying him.
Tom suffers a relapse of the measles the next day, and is bedridden for another three weeks. He recovers to find his friends have each also "suffered a relapse." They are back to misbehaving.
Twain draws a parallel between Tom's measles and the religious revival. Both are things that change and affect a person, but eventually pass on by.