Why is it important for a lawyer to take his or her responsibilities seriously? -

what are some possible consequences if a lawyer does not honor his or her responsibilities?

Because lawyers can be sued too.

Depending on the specific of what the lawyer had done (or not done) the penalties can range from a private reprimand, public reprimand, suspension of license to practice law, loss of license to practice law forever, monetary damages/fines, jail-time. Those offenses that would lead to jail time would have to be extremely egregious.