In Memories, dreams and reflections, Jung says of the manuscript of The Secret of the Golden Flower received from Richard Wilhelm:
"I immediately devoured the manuscript, for this text brought me an unsuspected confirmation concerning the mandala and the wandering around the center. This was the first event that broke through my solitude. I felt a kinship there that I could relate to. "
In reality, he saw much more than the mandala and the circumambulation, he found in it a symbolic description of the mystical experience he lived in June 1917. The Secret of the Golden Flower indeed states:
"If, while one is immersed in tranquility, the mind continually and uninterruptedly experiences a feeling of great elation, as if drunk or coming out of the bath, this is a sign that the luminous principle reigns harmoniously in the whole body; the golden flower bud then begins to form. If, in addition, all the openings remain calm, the silver moon stands in the middle of the sky and one has the feeling that the great earth is a world of light and clarity, it is a sign that the heart body is opening to clarity. It is a sign that the golden flower is opening."
Jung immediately understood that the golden flower is a chinese symbol for a mystical experience. To help you understand this description, a few explanations are necessary.
The feeling of great elation corresponds exactly to the joy that derives from the mystical experience. It is linked to the extreme numinosity of the event. Mystical experiences are always symbols of conjunction of opposites that impose themselves in consciousness. The text continues with the luminous principle. It corresponds to consciousness since references to light are always symbols of consciousness. Mystical experiences always happen in consciousness.
As one is completely absorbed by the experience, the openings (sight, hearing, smell, taste) remain calm. The paroxysmal experience is characterized by a lowering of the ego and an alteration of the spatio-temporal perception. This corresponds to the muting of the openings since the senses are not challenged during the mystical experience phenomenon.
It is the phrase "that the silver moon stands in the middle of the sky" that illustrates the symbol of conjunction of opposites. It requires further explanation as it is the heart of the experience.
In alchemy and hermetic texts, the moon is a symbol of matter and the sky or the sun is a representation of the spirit. This is also true with metals where gold always represents the sun and silver the moon. So when the silver moon stands in the middle of the sky, matter (the outside world) is contained within the mind. This is a very specific experience that corresponds to the philosopher's stone in alchemy. Although the experience is extremely rare, the best description that I have yet found, apart from mine, is from Forrest Reid (1875–1947). He described his mystical experience as follows:
“It was as if I had never realized before how lovely the world was. I lay down on my back in the warm, dry moss and listened to the skylark singing as it mounted up from the fields near the sea into the dark clear sky. No other music ever gave me the same pleasure as that passionately joyous singing. It was a kind of leaping, exultant ecstasy, a bright, flame-like sound, rejoicing in itself. And then a curious experience befell me. It was as if everything that had seemed to be external and around me were suddenly within me. The whole world seemed to be within me. It was within me that the trees waved their green branches, it was within me that the skylark was singing, it was within me that the hot sun shone, and that the shade was cool.”
The quote above from The Secret of the Golden Flower presents a beautiful image of that mystical experience: the silver moon (matter) stands in the middle of the sky (spirit). Jung depicted his corresponding mystical experience on page 125 of The Red Book. (The image is described in my paper below: Carl Jung's second mystical experience.)
The Secret of the Golden Flower also says that the great earth or the surrounding world is then illuminated with light: one understands everything. The body of the heart, i.e. the emotion of extreme numinosity, becomes more and more powerful in the face of this dazzling symbolmof conjunction of opposites and the golden flower (the mystical experience) opens up.
Carl Jung's Second Mystical Experience