"As a Man Thinketh" is a brief but powerful book that explores the connection between a person's thoughts and their destiny. James Allen argues that one's thoughts shape one's character, determine one's actions, and ultimately define one's destiny. The book stresses the importance of cultivating positive and constructive thoughts, as these lead to positive outcomes in life, while negative thoughts lead to negative outcomes.

Allen presents his message through clear and insightful metaphors and analogies, emphasizing personal responsibility and the ability of each individual to control his or her own destiny through conscious choice of thoughts. In addition, the author stresses the importance of self-discipline, self-control and perseverance on the road to goal achievement and personal fulfillment.