A symbol is an object that demands attention in itself but that also refers to another object or to a concept. Normal images and metaphors, through consistent use, may become symbols. Symbols may operate in more than one way at the same time, and often there is no one concept attached to a given object; instead, a whole range of ideas may be brought into play.
The tale of Silas Marner certainly must be understood symbolically as well as literally. Eppie is explicitly put forward as a substitute for Silas' treasure, and this raises questions of the nature of treasures literal and spiritual. Dunstan steals Silas' gold and in the process falls into a pit, but in another way the pit may be thought of as the pit that waits for all erring humans. Silas' door stands open as a symbol of his spiritual condition, and evil and good in turn come and work their influence on him. Silas' renewal of faith and human contact in this way becomes a symbolic rebirth. Both through his fits and through his alienation from other men, he is a man who has seemed dead and has come back to life.