The answer is quite simple. After all the years Silas Marner spends in forced isolation, obsessively gathering gold, and focusing on nothing but himself, he has a life changing event. Dunsey Cass, the wretched son of the town's squire, steals Silas's beloved gold and runs away.
When the situation occurs, we know that Silas went into a fit that concerned everyone in town, as he loses it so bad that he enters the Rainbow in a complete shock, and collapses there. This is because his life was like a formula. His formula was to collect gold, keep to himself, gratify his physical needs. All of this was geared to suppress the deep depression he still carries with him from his disgrace from Lantern Yard.
Yet, immediately after, in came baby Eppie; the child of Godfrey Cass and an opium fiend who dies on her way to Raveloe to confront the Epie's father. As Silas is away, his warm cottage serves as refuge to baby Eppie. Her gold hair, her innocent ways, and the fact that she is a baby who shows up out of nowhere in the middle of winter seem to strike the proverbial nerve in Silas once, he sees her. Notice how his entire personality changes at the site of a baby he does not even know. A typical person would have been shocked, scared, and anxious as to what to do with the child.
Silas, still dazed by the hit, but also a man inherently godly, finally comes out as who he really is: a true, loving creature who needs to be loved back, like once he was
Gold!—his own gold—brought back to him as mysteriously as it had been taken away! [...]He leaned forward at last and stretched forth his hand; but instead of the hard coin with the familiar resisting outline, his fingers encountered soft, warm curls.
It is cool to think of this scene. You can imagine he, trying to touch a cold, barren metal and, instead, feeling humanity for the first time in many years. A warm head, a human touch. Some of these things, he had never felt before in a while.
...Silas fell on his knees and bent his head low to examine the marvel; it was a sleeping child—a round, fair thing, with soft yellow rings all over its head. [...] That was the first thought that darted across Silas's blank wonderment.
Again, this encounter opens up an entire other side of Silas which the reader has never seen before. In fact, this event changes him forever, from the odd eye-balled enigmatic weaver, to a loving and kind adoptive father who is entirely enchanted by this baby girl, who grows up into a beautiful young lady, and who completes Silas's life for good. This is definitely how love triumphs over luxury.