marley adds a senseofstructure to the chaotic supernatural events that scrooge experiences, informing scrooge what to expect.
this is a dramatictechnique as readers expect and anticipate upcoming events, increasing tension.
dickens uses marley to introduce the reader to religious and supernatural themes.
he is the first ghost to appear, an arrival made more dramatic by the repetition of "old marley was dead". this heightens the impact of the supernatural theme as it makes his appearance unexpected.
dickens also employs him to establish the concept of religious justice , as dickens presents the idea of accountability through him.