Swami Vivekananda's illuminative ideas on religion are spread over nearly 4200 pages of his Complete Works. This book containing eight lectures is a compilation from the same and serves as a small introduction to his voluminous writings, talks, and lectures on the subject.
Change is always subjective. All through evolution you find that the conquest of nature comes by change in the subject. Apply this to religion and morality, and you will find that the conquest of evil comes by the change in the subjective alone. That is how the Advaitic system gets its whole force, on the subjective side of man.
-Swami Vivekananda