On Chapter 3 the story of the Cass clan comes to play in the story of Silas Marner when they introduce them and their roots. We know that they are a well-known clan who once enjoyed the pleasures of wealth and a good name, and that they are the proprietors of the Red House, which is considered in Raveloe as a place of high distinction within the parameters of the townsfolk.
The introduction of the Cass clan is necessary to the novel because it shows us that the Class clan has several weaknesses that actually may foreshadow an important crossing into the path of Silas Marner.
Among the weaknesses of the Cass clan are the brothers Godfrey and Dunsey. Godfrey, who needs desperately to marry for money, erroneously married a drug-addicted woman and hides it from his father who would kill him if he found out. Dunsley is money hungry and evil. We also know that Silas is hiding gold and that he is alone and quite vulnerable for people of this nature.
Hence, by letting us understand in full the nature of the Cass clan is how Elliot introduces their storyline into Silas's.