The crux of The Powers of the Mind by Swami Vivekananda focuses on the immense potential of the human mind and the importance of mastering it to achieve personal and spiritual growth. Swami Vivekananda explores how the mind, when trained and controlled, can unlock remarkable abilities and lead one toward self-realization. Here are the key points:

1. The Mind's Power: Swami Vivekananda emphasizes that the mind is the most powerful tool we possess. Our thoughts shape our actions, our perceptions, and ultimately our reality. By understanding and mastering the mind, one can overcome obstacles, achieve goals, and elevate the self.
2. Concentration and Willpower: A central theme is the importance of concentration and willpower. Swami Vivekananda teaches that by training the mind to focus and by cultivating a strong will, one can direct their energy toward achieving higher states of consciousness and success in life.
3. Mastering the Mind: Vivekananda stresses that the mind often leads to distractions and confusion, but through meditation, self-discipline, and detachment from the ego, we can gain control over it. Mastery over the mind is the key to self-realization and spiritual awakening.
4. Mental Conditioning: The book explores how our thoughts and mental habits shape our experiences. Swami Vivekananda advocates for the cultivation of positive, constructive thoughts, as they create harmony and a deeper connection with the universe.
5. The Role of Meditation: Meditation is presented as a powerful tool to quiet the mind, increase mental clarity, and develop higher levels of awareness. Through regular practice, one can sharpen the mind, increase concentration, and develop deeper spiritual insight.
6. The Mind and Spiritual Growth: Ultimately, The Powers of the Mind illustrates that the mind is not just a tool for achieving worldly success, but also for attaining spiritual enlightenment. By mastering the mind, one can transcend the limitations of the ego and experience unity with the divine.

In essence, the crux of the book is the idea that by understanding, controlling, and harnessing the powers of the mind, individuals can unlock their full potential, achieve personal growth, and attain spiritual liberation.