Essentially these three chapters serve to tell us more about each of the three musketeers. Chapter 25 gives us additional information about the vain Porthos, Chapter 26 shows us Ararmis's conflict between love and religion, and Chapter 27 tells us more about Athos's past, which haunts him and drives him to excessive drinking.
While reading Chapter 25, we should remember that d'Artagnan first encountered Porthos when he collided with him on a stairwell and, by accident, it was revealed that Porthos was wearing a golden shoulder belt that was only half gilded. In that encounter, injured vanity was the principal reason why Porthos challenged d'Artagnan to a duel. Likewise, in this chapter, the emphasis is again on Porthos's extreme vanity. As noted in the summary, Porthos cannot admit that he was bested in a duel. Likewise, he feels that he needs to brag about his young and beautiful "duchess" when, in reality, his "duchess" is a fiftyish wife of a lawyer. Yet note that d'Artagnan although a young man, is astute enough not to mention the truth to Porthos; he allows Porthos to continue with his fantasies.
Although Dumas revealed to us earlier that Monsieur Bonacieux assisted in his wife's abduction, it is only in Chapter 25 that d'Artagnan becomes fully aware of this fact. Remembering the description given to him of the fat little man, he looks at Bonacieux's shoes and realizes that he and Bonacieux have the same kind of red mud on their shoes. "At the same time he also noticed Bonacieux's shoes and stockings: they were spotted with exactly the same kind of mud. An idea flashed into his mind: that short, fat, gray-haired man, treated without respect by the noblemen who abducted Madame Bonacieux, was Bonacieux himself! The husband had taken part in his wife's abduction!" D'Artagnan concludes that Bonacieux is a miserable scoundrel.
