The allegory of the spoiled prince
This is a story modeled after the story of the Buddha who was spoiled by his father so he would not have to know the darkness and suffering of the world. In both cases, tragedy strikes, but interestingly, this novel includes another character, Franklin, who shows the ultimate fate for Henry if life had not forced tragedy upon Henry. Ironically, the spoiling is the bad thing for Henry, and the tragedy is actually helpful in his maturation.
The mountain climber
When Franklin is comatose, he suddenly raises up and looks at Henry, telling him, "Katahdin," before laying back down to die. That's the name of the mountain they agreed to climb together, so Henry takes this pilgrimage as a way to honor his brother. The journey toward the summit is simultaneously a metaphor for Henry's growth toward adult independence, religious awakening, and forgiveness.
The failed brother
This is not to suggest that Franklin ever deserved his death, and it's wrong to say that Franklin's moral corruption is perfectly "his fault" because his dad co-conspired by spoiling Franklin with limitless money and luxury. Nevertheless, Louisa teaches Henry that behind closed doors, Franklin was becoming hateful toward the poor, and he was even demonstrating early signs of racism. Franklin represents the actual result of their father's plan to protect the boys: It leads to moral corruption or "spoiling."
The best friend
Henry needs a mirror to help him analyze his life more objectively. Sanborn is extremely helpful in this regard, because as they climb, the compare notes about their spoiled childhood, and Henry realizes that without allowing a child to see the good with the bad, they become hollow and shallow instead of having the depth of character they might have had if they didn't have their money to protect them.
The holy sister
One interesting way of viewing Henry's sister Louisa is as a spiritual guide, the same way Dante often used women companions in his Comedy. Louisa's role is to help Henry to see the facts about his life in a new light. What Henry means when he decides to climb the mountain in his brother's honor is that he wants to participate in Franklin's legacy, but Louisa subverts this as his main goal by showing that Franklin was a regular person, not a hero, and that he was sometimes hateful and racist. In other words, Louisa is allowing Henry to adjust his point of view through wisdom. She seems to represent Henry's potential to honor his brother in a different, better way, by becoming a good person.
