What is the purpose of repeating that Marley is dead?

Through this repetition, the reader comes to understand the supernatural element in the story. Marley's face appears everywhere.... and yet, he isn't alive. He is in Scrooge's thoughts.... in the present.

Scrooge himself is stuck in the present.... stuck in time, the nature of capitalism, and the constant concern of what can be done "now" to accumulate more money. Scrooge's world revolves around the time, how much time has past, and how much time is left to line the coffers. Fred represents the idea that Christmas is a time to relax, enjoy, and be with family. Scrooge sees it as a waste and detriment to what can be acomplished.