The phrase rat race makes a reference to a lifestyle in which people are constantly tied to a time-consuming job because they have many debts to pay. This becomes a vicious cycle because they always spend more money than what they can afford. They live their lives in a constant struggle while trying to fix their financial status. Therefore, the correct answer is that a rat race is a useless struggle.
The purpose is for the author to make the reader want to read and find out more since most likely the first book ended in a cliff hanger; they want the reader to read more and find out more of what will happen.