Scrooge's fiancee, Belle, tells him sadly that a "golden idol" has replaced her and become first in his heart. She tells him he has become too obsessed with making money.
He replies that there is nothing the world is so hard on as poverty; there is nothing the world pretends ("professes") to condemn as much as the pursuit of wealth. In other words, he is telling her that there is nothing wrong with trying to make money.
Belle responds that Scrooge is too fearful of the world. She says he has dropped all his "nobler aspirations" and become fixated on gain.
She also tells him that she can sense he now regrets becoming engaged to her, a poor young woman, and wishes he were free to marry someone wealthy. Scrooge can't absolutely deny this, so Belle releases him from his engagement with her, something he doesn't try to prevent.
In short, Belle thinks Scrooge has become too obsessed with money because he is fearful of what the world will do to him should be become poor. He is driven by a negative emotion, fear, that has erased all his positive feelings and made him single-minded in his pursuit of wealth.