George Eliot made this comment in a letter she wrote at the same time she was composing Silas Marner. It is a typical Eliot sentiment, as she believed her whole life that people could not get reach their fullest potential without caring about something beyond themselves or their own material comfort. In this quote, she states that a person who starts to hope in something more than himself ("a faith or an idea") will live a fuller and deeper life (achieve "a higher order of experience.")
We can see the contrast in how the two characters, Silas and Godfrey, live out this principle. Silas undergoes a long period of disillusionment after he is framed for a theft he did not commit and cast out of his church because of a superstitious ritual. For many years, he lives for himself and for earning money, valuing the gold he hoards more than people. However, all of this changes when little Eppie, hardly more than a toddler, crosses his path by stumbling into his door on a snowy evening. Once he devotes himself to her, Silas's life changes for the better, growing spiritually richer as he turns his love toward her and away from money. The idea he embodies is captured in the Wordsworth quote Eliot uses at the beginning of the book:
A child, more than all other gifts
That earth can offer to declining man,
Brings hope with it, and forward-looking thoughts.
While Silas's devotion to a child transforms his life and soul, giving him something to love beyond himself, renewing his faith in God, and orienting him with hope toward the future, Godfrey, however, rejects this path, though he is a well-intentioned person. Eppie is his biological daughter, but he cares more about his own material comfort and status than he does her. He does not want to claim her as his own because he fears being disinherited, which will leave him without the money and "stuff" to which he has grown accustomed. He is a morally weak man who is afraid to rock the boat, despite all he owes to Eppie as her father.
Godfrey wasn't afraid to seduce Eppie's poor mother and impregnate her, but he is afraid to accept the consequences of this act. Godfrey therefore allows Dunstan to blackmail him. It is only after he knows that Dunstan is dead that Godfrey feels safe enough to step forward and try to claim Eppie.
But his conviction that Eppie will be delighted to become his daughter because of his status as a wealthy gentleman with much more to offer her materially than Silas shows that Godfrey doesn't "get" that money and social position are not what really counts in life. Eppie has the solid moral foundation to reject Godfrey's wealth in favor of the humbler man who has been a real father to her and given her the real wealth of true love. Godfrey has been unable to find faith in an idea of a higher order than the material and pays the price in a stunted life and the loss of the love he could have had.
As Eliot writes in another novel, Adam Bede, "Our deeds determine us, as much as we determine our deeds." Silas did the good deed in raising Eppie; Godfrey did not and loses out.