This treatise, although it is not so much a personal confession as a description of the golden age of alchemy, nevertheless tells us how the alchemist imagined the psychological structure of his opus.
Its association with the invisible forces of the psyche was the real secret of the magisterium.
In order to express this secret the old masters readily resorted to allegory.
One of the oldest records of this kind, which had a considerable influence on the later literature, is the “Visio Arislei,” and its whole
character relates it very closely to those visions known to us from the psychology of the unconscious.
As I have already said, the term imaginatio, like meditatio, is of particular importance in the alchemical opus.
Earlier on we came across that remarkable passage in the Rosarium telling us that the work must be done with the true imaginatio, and we saw elsewhere [par. 357] how the philosophical tree can be made to grow through contemplation (figs. 131, 135).
Ruland’s Lexicon once more helps us to understand what the alchemist meant by imaginalio. ~Carl Jung, CW 12, Para 392-393