The main thesis of the book is that happiness and inner peace are not dependent on external circumstances, but rather on one's own thoughts and beliefs. Hall argues that in order to achieve an untroubled mind, it is necessary to cultivate positive and constructive thoughts, and to let go of negative and self-defeating patterns of thinking.

The book provides practical guidance on how to cultivate a positive mental attitude, including techniques for mindfulness, visualization, and affirmation. Hall also discusses the importance of developing healthy habits, such as exercise and nutrition, and of taking responsibility for one's own well-being.

?One of the key themes of the book is the importance of self-awareness and self-discovery. Hall encourages readers to take the time to reflect on their own thoughts and beliefs, and to develop a deeper understanding of themselves and their connection to the world around them.

Overall, "The Untroubled Mind" is a motivational work that offers practical guidance for achieving inner peace and happiness. While some of the language and ideas in the book may seem outdated to modern readers, the principles outlined in the book are still relevant today and can be applied to anyone's life, regardless of their background or circumstances. The book provides practical advice and guidance for achieving an untroubled mind and creating a fulfilling life through positive thinking and self-awareness.