The book "The Gospel of Wealth" by Andrew Carnegie discusses the responsibility of the wealthy to use their fortunes for the benefit of society. Carnegie argues that the rich should engage in philanthropy and address social issues, emphasizing that wealth should be distributed for the greater good. The key ideas include the concept of "surplus wealth," the idea that the wealthy should be trustees of their wealth for public welfare, and the belief that philanthropy can help mitigate the negative effects of inequality. The book is significant in the context of philanthropy and wealth distribution as it influenced a generation of philanthropists and contributed to the development of modern philanthropic practices in the United States.