The book, written in 1963, is based on what the author calls the ‘duality of mind’ and in turn on what he refers to as the universal law of action and reaction:
The thought in my conscious mind, good or bad, is incipient action. The reaction is the response from my subconscious mind which always corresponds exactly with the nature of my thought in my conscious mind.

The following are basically quotes taken from different pages of the book.

According to Joseph Murphy, there is only one mind, but it possesses two distinctive characteristics. Or, there are two levels of one mind – the conscious or rational level, and the subconscious or irrational level. They are merely two spheres of activity within one mind.

Some other terms used for the conscious and subconscious mind are: the objective and subjective mind, the waking and sleeping mind, the surface self and the deep self, the voluntary and involuntary mind, the male and the female, etc.

According to the author, with my conscious mind I think, good or bad, and whatever I habitually think sinks down into my subconscious mind. In response, the subconscious mind, being all-powerful and omnipotent, creates my life experiences exactly as per my thoughts that sank into it. In other words, whatever idea I claim mentally and feel as true (even if it is actually wrong and happens to be a negative idea), my subconscious mind will accept it as it is, bring it forth into my experience and execute it exactly. For example, a young singer was invited to give an audition. She had a very good voice, but she had been repeatedly saying to herself, “When the time comes for me to sing, maybe they won’t like me. I will try, but I am full of fear and anxiety.” Her subconscious mind accepted it as a request and proceeded to manifest them and bring them into her experience. The cause of her failure was silent fear thoughts emotionalized and subjectified.

A knowledge of the interaction of my conscious and subconscious minds will enable me to transform my whole life.

When my mind thinks correctly, when I understand the truth, when the thoughts deposited in my subconscious mind are constructive, harmonious, and peaceful, the magic working power of my subconscious will respond and bring about harmonious conditions, agreeable surroundings, and the best of everything. When I begin to control my thought processes, I can apply the powers of my subconscious to any problem or difficulty.

Every thought is a cause, and every condition is an effect. For this reason, it is essential that I take charge of my thoughts so as to bring forth only desirable conditions. If I think good, good will follow; if I think evil, evil will follow. Hence the importance of selecting thoughts, ideas and premises which bless, heal, inspire, and fill my soul with joy.