Carl Jung's most important work is not Red Book.

     The Red Book documents Jung's personal dreams, visions, and spiritual journey, essentially serving as a private journal of self-healing. Jung did not wish for it to be published during his lifetime, keeping it locked in a bank vault as a personal item.

     The creation of the Red Book was born out of a particular set of circumstances. It's important to understand that a central tenet of Jungian psychology is the concept of the collective unconscious, which distinguishes Jung's analytical psychology from Freud's psychoanalysis. However, when Jung and Freud parted ways in 1913, Jung's theory of the unconscious was not yet fully formed. Moreover, due to Freud's authoritative position in psychology at the time, Jung's theories faced widespread and severe criticism. After that, aside from publishing "Psychological Types" in 1921, Jung made little academic progress. Despite embarking on a series of travels, these did not alleviate his sense of loss and suffering. In the opening part of his autobiography, "Memories, Dreams, Reflections," Jung wrote about the period after his split with Freud: "For a long time, I felt as if I were a defeated general without an army. I had no idea what to do. I was completely suspended in the air; I had no foothold."

     Despite this sense of disorientation, Jung did not cease his research and contemplation of psychology. In 1914, he began to work on what would become the Red Book, writing down significant visions and illustrating them with his own abstract drawings. At this point, Jung could not yet provide an accurate or complete definition of the collective unconscious. Thus, the Red Book laid the groundwork for a whole set of analytical psychological theories, including archetypes and the collective unconscious.

     Then, in 1927, the Chinese scholar Richard Wilhelm sent Jung his newly translated "The Secret of the Golden Flower" and asked him to write a commentary on this Chinese Taoist text. Jung was deeply moved and enlightened by this book, believing he had found the true source of the collective unconscious within it (at the time, it was only a translation and not yet published). He wrote an extensive commentary and, by the end of 1929, co-published "The Secret of the Golden Flower" with Wilhelm (in German). "The Secret of the Golden Flower" consists of two parts: one is the Chinese translation of "The Secret of the Golden Flower," and the other is Jung's lengthy commentary.

     In summary, while the Red Book is a significant work that reflects Jung's personal exploration and development of his psychological theories, it is not considered his most important book. Instead, "The Secret of the Golden Flower," with its combination of Chinese philosophical text and Jung's psychological insights, is often regarded as one of his most crucial contributions to the field of analytical psychology.