In order to understand Silas's reaction to his gold, one must go back into the novel and remember how Silas ended up in Raveloe in the first place. Silas was once a very normal and active man. He was engaged to marry, had friends, and was even a community leader in the town of Lantern Yard. The betrayal of his best friend caused in Silas an overall disappointment with people. Not only had this best friend falsely accused Silas of theft, but he stained his reputation in Lantern Yard. Not enough with that, this friend also took Silas's fiancee!
The situation made Silas feel as if the foundation upon which he had based a life had just quickened below his feet. He had to start over, and forget forever his life at Lantern Yard. Although Silas somewhat connects with the people of Raveloe, it is the gold what ultimately isolated him from his fellow citizens for once and for all. Granted, Silas acts with his gold the way hoarders often do: collecting vast amounts of things to make up for a very empty feeling; in this case, it is his loneliness what prompts Silas to focus on building up a sort of goldmine for himself.
His gold, as he hung over it and saw it grow, gathered his power of loving together into a hard isolation like its own.
Silas is not even that interested on what the gold would bring, but merely on the fact of having it. This is a very intense form of greed but, like the narrator states, Silas Marner is such a harmless man that even greed would not be such a bad thing in his case.
Yet few men could be more harmless than poor Marner. In his truthful, simple soul not even the growing greed and worship of gold could beget any vice directly injurious to others.
However, he was indeed getting greedy. Even when his greed is a result of sadness and loneliness, it sees to be taking a good hold of his daily life.
Supper was his favorite meal, because it came at his time of revelry, when his heart warmed over his gold
In all, Silas does change as a result of the gold. The gold fills up the gap left by the betrayal of his friends from Lantern Yard. The gold gives Silas a false sense of happiness and fulfillment which, in turn, isolates him even more from the rest of his society. Any type of isolation is bad enough, but when the isolation is fed by a vice, or by a bad habit such as hoarding, it becomes worse. When the gold is stolen and Silas falls into a nervous breakdown, he awakes and becomes a better person after all.