The shoes were what the Witch lusted after...A token of rememberance? Were they, really? Perhaps.

Dorothy wore them and remembered Kansas. Nessa wore them and remembered Father, a glimpse of Mother, and Boq. Elphaba did not wear them.

Were they a symbol of power? Yes. Nessa was the Governess, and she wore them. She was about to set the Munchkins free when the house crashed down.

A passing Munchkin was said to have made the crushing a joke.

Question: What was the last thing to go through the Witch's mind?

Answer: Dorothy's front door.

It was those shoes that killed the Witches. The shoes made Nessa walk, and that led to her stealing Boq's heart. The shoes were Dorothy's passport into the Emerald City; The Wizard saw the shoes and sent Dorothy to kill.

Those shoes were what made Elphaba become the Witch. Those gleaming, happy, ruby shoes...red like the blood they spilled.