It's almost like an essay. I swear this was not intentional (might have been out of habit). On a side note I learned everything I know about the Major Arcana from a game I played two years ago.
This is addressing both the actual 'Joker' and the events of the book.
JOKER & THE FOOL
‘What’s in it for Ed Kennedy?’(p 222)
It's not hard to see that the Joker is the most unique of a full set of playing cards. The Aces all had their own meanings but the Joker is much more symbolic and ambiguous in meaning.
Born from the concept of a 'wild card' that could beat even the highest values of deck, the Joker originated from a tarot card of the Major Arcana. This card is known as the Fool (or the Jester).
The Major Arcana consists of 22 trump cards used by fortune tellers to tell your fortune. Though all other cards in the Arcana are numbered from 1-21, the Fool never took on its own number. This is similar to how the Joker is not shown to belong to any suit. Later editions of the Fool shows it with the number 0 or 22; the beginning and the end, the first and the last. This may be representative of Ed's initial incompetence, and his self-improvement as the story went on and his messages were delivered.
The true worth of the Joker only arises in the event of challenge. Ed's journey only consists of challenge after challenge. The true meaning of the Joker is summed up in a single quote near the end of the book. “If a guy like you can stand up and do what you did, then maybe everyone can. Maybe everyone can live beyond what they're capable of.” (p 382) The Joker and the Fool are symbolic of having infinite possibilities. Throughout the text this is in the form of Ed's personal growth.
Ultimately, Ed realizes that this entire time he wasn't just fixing other people's lives and helping them. The only person who needed help was him. “I'm not the messenger at all. I'm the message.” (p 386)