Bob Cass is the last of Squire Cass's sons in Silas Marner. You may also already know, by know, that the other two children, Dunstan and Godfrey, are good for nothing. Therefore, Bob, who hardly participates in the novel, is described as Squire Cass's "favorite" son. As the youngest, he is described by the butcher as "just a boy". Bob's favorite qualities are real to the brothers, as well. They know that they should follow in Bob's steps in order to be liked more by their father.
Speaking of Bob's ways, we do get a glimpse of him in chapter XIII, when Squire Cass admires his musical talents
Bob Cass was figuring in a hornpipe, and his father, very proud of this lithe son, whom he repeatedly declared to be just like himself in his young days .
In this chapter we know that Squire Cass invites others to see his son perform, and that Squire is incredibly proud of him in many ways. He sees himself in Bob, which is something he has tried to do in his eldest, Godfrey, to no avail. We know that the problem is middle child Dunstan, who influences the weak Godfrey without mercy, and always toward the negative. The fact that Godfrey has taken up with an opium fiend, and has fathered a child with her, is something that Squire Cass still has not found out about. Therefore, it is clear that Bob would provide the comfort and hope that the other two sons have failed to help their father get.