Mr. Farebrother is a vicar in Middlemarch. He's a fun guy to hang around – he likes biology more than making sermons, and he's always down for a game of cards. Unfortunately, he's a little too fond of the cards, and plays for money – not something a clergyman should do. But he's got an old mother, an unmarried aunt, and an unmarried sister to take care of on a small salary. So what's a guy to do? He's good at cards, and can make up the difference in his salary by playing whist at fancy dinner parties.
Overall, Farebrother is a good guy. Once he gets a better job (thanks to Dorothea and Lydgate), he gives up the gambling. But that wasn't the major sacrifice of the novel: he also gives up all hopes of marrying Mary Garth when he finds out she likes Fred Vincy.