Silas begins the book fully part of his Lantern-Yard group and then spends the next fifteen years living alone in a cottage, rejecting anyone's attempt to bring him into village life. If we think of Silas Marner as a religious allegory, then we can think of the story as the soul being taken away from God and then brought back to it. Or if Silas Marner is Eliot's attempt to think about England and history, then it's the story of England becoming a nation, all the little isolated pockets of communities beginning to see themselves as part of a country connected by a common culture and brought together by railroads—and being destroyed in the process. Leaving isolation is not always good.
In Silas Marner, individuals pass through isolation as a necessary stage along the way to true community.
Eliot suggests that isolation is destructive, leading to crime and debasement.