The Meditations of Marcus Aurelius contains timeless moral exhortations, devotional reflections, guidance towards self-improvement, and pious acknowledgements of Man's natural duties. It teaches its reader to reason with his own self, bear with others, revere the gods and accept the will of Providence, fulfill his natural duties, serve his fellow man, strive only for virtue for virtue's sake and to conquer vice. It is a book whose lessons are as relevant today as they were nearly 1800 years ago when it was written, and can be used by the rich and the poor, the powerful and the powerless, and every station in between.
But Emperor Marcus Aurelius was not writing for us, for posterity, or even for his contemporaries. He was writing to himself. The most powerful man on the earth, a man who could have his every command obeyed and could have lived in unspeakable pleasure and luxury, chose instead to write for himself a moral compass; a book which would remind him about piety, duty, service, compassion, temperance, fortitude, and a entire host of other virtues and responsibilities.
The Meditations are divided into twelve chapters normally called "Books" (thus, Book 1, Book 2, etc). Each Book contains short passages which are essentially messages that Marcus wrote to himself. These passages are themselves numbered (thus, Book 1:1, 1:2, 1:3, and so on). They cover a variety of ethical topics. Simply put, this was Marcus's moral notebook.