This book is a practical and theological guide to the contemplative and mystical life. The author explains the secret path by which the human soul, through purification and profound love, is prepared to achieve intimate union with God. The work focuses on the direct experience of the 'sacred operation of the Holy Spirit' within the soul, going beyond mere intellectual meditation. The author emphasizes the importance of the soul's gradual preparation to receive divine grace. This involves self-abnegation, inner silence, and the surrender of one's will to the divine will. He explains how the soul moves from vocal prayer to silent mental prayer/contemplation. The essence of the book focuses on the mystical path to union with God. The book emphasizes that prayer is speaking to God with the heart. The author encourages readers to focus not only on words but also on igniting inner affection, focusing all intentions on union with God through pure and intense love. The purpose of this book is to explain the true meaning of the contemplative life, maintaining a healthy mysticism, while correcting errors such as extreme quietism.